Solucao Calculo 5ed CAP.4

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(1)Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 1. A function f has an absolute minimum at x=c if f (c) is the smallest function value on the entire domain of f , whereas f has a local minimum at c if f (c) is the smallest function value when x is near c . 2. (a) The Extreme Value Theorem (b) See the Closed Interval Method. 3. Absolute maximum at b ; absolute minimum at d ; local maxima at b and e ; local minima at d and s; neither a maximum nor a minimum at a , c , r , and t . 4. Absolute maximum at e ; absolute minimum at t ; local maxima at c , e , and s ; local minima at b , c , d , and r ; neither a maximum nor a minimum at a . 5. Absolute maximum value is f (4)=4 ; absolute minimum value is f (7)=0 ; local maximum values are f (4)=4 and f (6)=3 ; local minimum values are f (2)=1 and f (5)=2 . 6. Absolute maximum value is f (8)=5 ; absolute minimum value is f (2)=0 ; local maximum values are f (1)=2 , f (4)=4 , and f (6)=3 ; local minimum values are f (2)=0 , f (5)=2 , and f (7)=1 . 7. Absolute minimum at 2, absolute maximum at 3, local minimum at 4. 8. Absolute minimum at 1, absolute maximum at 5, local maximum at 2, local minimum at 4. 9. Absolute maximum at 5, absolute minimum at 2, local maximum at 3, local minima at 2 and 4. 1.

(2) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 10. f has no local maximum or minimum, but 2 and 4 are critical numbers. 11. (a). (b). (c) 12. (a) Note that a local maximum cannot occur at an endpoint.. 2.

(3) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. (b). Note: By the Extreme Value Theorem, f must not be continuous. 13. (a) Note: By the Extreme Value Theorem, f must not be continuous; because if it were, it would attain an absolute minimum.. (b) 14. (a) 3.

(4) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. (b) 15. f (x)=83x , x 1 . Absolute maximum f (1)=5 ; no local maximum. No absolute or local minimum.. 16. f (x)=32x , x 5 . Absolute minimum f (5)=7 ; no local minimum. No absolute or local maximum.. 2. 17. f (x)=x , 0<x<2 . No absolute or local maximum or minimum value.. 4.

(5) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 2. 18. f (x)=x , 0<x 2 . Absolute maximum f (2)=4 ; no local maximum. No absolute or local minimum.. 2. 19. f (x)=x , 0 x<2 . Absolute minimum f (0)=0 ; no local minimum. No absolute or local maximum.. 2. 20. f (x)=x , 0 x 2 . Absolute maximum f (2)=4 . Absolute minimum f (0)=0 . No local maximum or minimum.. 2. 21. f (x)=x , 3 x 2 . Absolute maximum f (3)=9 . No local maximum. Absolute and local minimum f (0)=0 .. 5.

(6) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 2. 22. f (x)=1+(x+1) , 2 x<5 . No absolute or local maximum. Absolute and local minimum f (1)=1 .. 23. f (t)=1/t , 0<t<1 . No maximum or minimum.. 24. f (t)=1/t , 0<t 1 . Absolute minimum f (1)=1 ; no local minimum. No local or absolute maximum.. 25. f ( )=sin , 2 2 . Absolute and local maxima f local minima f. . 2. =f. 3 2. . 3 2. =f. 2. =1 . Absolute and. =1 .. 6.

(7) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. < . Absolute minimum f 4 2. 26. f ( )=tan , . . 4. =1 ; no local minimum. No absolute. or local maximum.. 27. f (x)=1 x . Absolute maximum f (0)=1 ; no local maximum. No absolute or local minimum.. x. 28. f (x)=e . No absolute or local maximum or minimum value.. 29. f (x)=. {. 30. f (x)=. {. 1x if 0 x<2 2x4 if 2 x 3 Absolute maximum f (3)=2 ; no local maximum. No absolute or local minimum.. 2. if1 x<0. x. 2. 2x. if0 x 1 7.

(8) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. Absolute and local maximum f (0)=2 . No absolute or local minimum.. 2. /. /. 31. f (x)=5x +4x f (x)=10x+4 . f (x)=0 x= 3. 2. /. 2. 2 2 , so is the only critical number. 5 5. /. 32. f (x)=x +x x f (x)=3x +2x1 . f (x)=0 (x+1)(3x1)=0 x=1 ,. 1 . These are the only 3. critical numbers. 3. 2. /. (. 2. ). 2. 33. f (x)=x +3x 24x f (x)=3x +6x24=3 x +2x8 . /. f (x)=0 3(x+4)(x2)=0 x=4 , 2 . These are the only critical numbers. 2 412 3 2 / 2 / 2 34. f (x)=x +x +x f (x)=3x +2x+1 . f (x)=0 3x +2x+1=0 x= . Neither of these is 6 a real number. Thus, there are no critical numbers. 4. 3. 2. /. 3. 2. (2. /. ). 2. 35. s(t)=3t +4t 6t s (t)=12t +12t 12t . s (t)=0 12t t +t1 t=0 or t +t1=0 . Using the 2. 1 1 4(1)(1) 1 5 = 0.618 , quadratic formula to solve the latter equation gives us t= 2(1) 2 1 5 1.618 . The three critical numbers are 0 , . 2 36. f (z)=. z+1 2. f. z +z+1. /. 2 2 ( z +z+1 )1(z+1)(2z+1) z 2z (z)= = =0 z(z+2)=0 z=0 , 2 are the 2 2 2 2 ( z +z+1) ( z +z+1) 2. critical numbers. (Note that z +z+1 0 since the discriminant <0 .). 37. g(x)= 2x+3 = /. {. 2x+3 if 2x+3 0 g (x)= (2x+3) if 2x+3<0 /. {. 3 2 3 2 if x< 2. 2. if x>. /. g (x) is never 0 , but. g (x) does not exist for 8.

(9) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. x=. 3 3 , so is the only critical number. 2 2 1/3. 38. g(x)=x x /. 2/3. /. g (x)=. 1 2/3 2 5/3 1 5/3 x+2 x + x = x (x+2)= . 5/3 3 3 3 3x. /. g (2)=0 and g (0) does not exist, but 0 is not in the domain of g , so the only critical number is 2 . 2/3. 39. g(t)=5t +t /. g (t)=. 5/3. /. g (t)=. 10 1/3 5 2/3 / t + t . g (0) does not exist, so t=0 is a critical number. 3 3. 5 1/3 t (2+t)=0 t=2 , so t=2 is also a critical number. 3. 40. g(t)= t (1t)=t. 1/2. t. 3/2. /. g (t)=. 1. . 3 / t . g (0) does not exist, so t=0 is a critical number. 2. 2 t 13t 1 1 t= , so t= is also a critical number. 0=g (t)= 3 3 2 t /. 4/5. 2. 41. F(x)=x (x4) 4/5 2 4 1/5 1 1/5 / F (x) =x 2(x4)+(x4) 5 x = 5 x (x4) 5 x 2+(x4) 4 8 / (x4)(14x16) 2(x4)(7x8) = = =0 when x=4 , ; and F (0) does not exist. 1/5 1/5 7 5x 5x. 8 ,4. 7. Critical numbers are 0 ,. 1 2 2/3 / 2 x x (2x1) . G (x) does not exist when x x=0 , that is, when 3 1 1 / x=0 or 1 . G (x)=0 2x1=0 x= . So the critical numbers are x=0 , ,1. 2 2 3. 42. G(x)=. 2. (. /. x x G (x)=. 2. ). /. /. 43. f ( )=2cos +sin f ( )=2sin +2sin cos . f ( )=0 2sin (cos 1)=0 sin =0 or cos =1 =n ( n an integer) or =2n . The solutions =n include the solutions =2n , so the critical numbers are =n . /. 2. /. 2. 44. g( )=4 tan g ( )=4sec . g ( )=0 sec =4 sec = 2 cos =. 1 = +2n , 2 3 9.

(10) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 5 2 4 +2n , +2n , and +2n are critical numbers. 3 3 3 /. Note: The values of that make g ( ) undefined are not in the domain of g . /. 1. /. 45. f (x)=xln x f (x)=x(1/x)+(ln x) 1=ln x+1 . f (x)=0 ln x=1 x=e =1/e . Therefore, the only critical number is x=1/e . 2x. /. 2x. 2x. 2x. 2x. 46. f (x)=xe f (x)=x(2e )+e =e (2x+1) . Since e 1 1 2x+1=0 x= . So is the only critical number. 2 2 2. /. is never 0 , we have f (x)=0 only when. /. 47. f (x)=3x 12x+5 , 0,3 . f (x)=6x12=0 x=2 . Applying the Closed Interval Method, we find that f (0)=5 , f (2)=7 , and f (3)=4 . So f (0)=5 is the absolute maximum value and f (2)=7 is the absolute minimum value. 3. /. 2. 48. f (x)=x 3x+1 , 0,3 . f (x)=3x 3=0 x= 1 , but 1 is not in 0,3 . f (0)=1 , f (1)=1 , and f (3)=19 . So f (3)=19 is the absolute maximum value and f (1)=1 is the absolute minimum value. 3. 2. /. (. 2. ). 2. 49. f (x)=2x 3x 12x+1 , [2,3] . f (x)=6x 6x12=6 x x2 =6 ( x2 ) ( x+1 ) =0 x=2,1 . f (2)=3 , f (1)=8 , f (2)=19 , and f (3)=8 . So f (1)=8 is the absolute maximum value and f (2)=19 is the absolute minimum value. 3. 2. /. 4. 2. /. )3. /. (. 2. ). 2. 50. f (x)=x 6x +9x+2 , [1,4] . f (x)=3x 12x+9=3 x 4x+3 =3(x1)(x3)=0 x=1,3 . f (1)=14 , f (1)=6 , f (3)=2 , and f (4)=6 . So f (1)= f (4)=6 is the absolute maximum value and f (1)=14 is the absolute minimum value.. (. 3. 2. ). 51. f (x)=x 2x +3 , [2,3]. f (x)=4x 4x=4x x 1 =4x(x+1)(x1)=0 x=1 , 0 , 1 . f (2)=11 , f (1)=2 , f (0)=3 , f (1)=2 , f (3)=66 . So f (3)=66 is the absolute maximum value and f ( 1)=2 is the absolute minimum value.. (. 2. (. 2. )2. 2. 2. 52. f (x)= x 1 , [1,2] . f (x)=3 x 1 ( 2x ) =6x ( x+1 ) ( x1 ) =0 x=1,0,1 . f ( 1)=0 , f (0)=1 , and f (2)=27 . So f (2)=27 is the absolute maximum value and f (0)=1 is the absolute minimum value.. 53. f (x)=. x 2. x +1 , f (1)=. , 0,2 . f. /. 2 2 ( x +1 ) x(2x) 1x (x)= = =0 x= 1 , but 1 is not in 2 2 2 2 ( x +1) ( x +1). 0,2 . f (0)=0. 1 2 1 , f (2)= . So f (1)= is the absolute maximum value and f (0)=0 is the absolute 2 5 2 10.

(11) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. minimum value. 2. x 4. 54. f (x)=. 2. , [4,4] . f. /. x +4 f (0)=1 . So f ( 4)=. and. 3 is the absolute maximum value and f (0)=1 is the absolute minimum value. 5. 2. 4t , 1,2 .. 55. f (t)=t. 1 2 f (t)=t 4t 2. (. /. 2 2 ( 12 3 x +4) (2x) ( x 4) (2x) 16x (x)= = =0 x=0 . f ( 4)= = 2 2 20 5 2 2 ( x +4) ( x +4). 2. ). 1/2. ( 2t ) + ( 4t. 2 1/2. ). 1=. t. 2. 2. + 4t =. 4t. 2. (. t + 4t. 2. 4t. 2. )=. 42t. 2. 2. 4t. 2. /. . f (t)=0 2. /. 42t =0 t =2 t= 2 , but t= 2 is not in the given interval, 1,2 . f (t) does not exist if 2. 4t =0 t= 2 , but 2 is not in the given interval. f (1)= 3 , f ( 2 ) =2 , and f (2)=0 . So f ( 2 ) =2 is the absolute maximum value and f (1)= 3 is the absolute minimum value. 3. 56. f (t)= t ( 8t ) , [0,8] . f (t)=8t. 1/3 4/3. t. /. f (t)=. /. . f (t) does not exist if t=0 . f (0)=0 , f (2)=6 So f (2)=6. 3. 3. 8 2/3 4 1/3 4 2/3 / 4(2t) t t = t (2t)= . f (t)=0 t=2 3 2 3 3 3 3 t. 2 7.56 , and f (8)=0 .. 2 is the absolute maximum value and f (0)= f (8)=0 is the absolute minimum value.. 57. f (x)=sin x+cos x ,. 0,. 3. /. . f (x)=cos xsin x=0 sin x=cos x. 3 +1 = 2 1.41 , f = 1.37 . So f . f (0)=1 , f 2 4 4 3 maximum value and f (0)=1 is the absolute minimum value. x=. /. 58. f (x)=x2cos x , , . f (x)=1+2sin x=0 sin x= f. . 5 6. = 3. 5 0.886 , f 6. absolute maximum value and f x. /. . . 6. x. 6. = =. x. sin x =1 tan x=1 cos x. 4. = 2 is the absolute. 5 1 x= , . f ( )=2 1.14 , 6 6 2. 3 2.26 , f ( )= +2 5.14 . So f ( )= +2 is the 6. 3 is the absolute minimum value. 6 x. 59. f (x)=xe , 0,2 . f (x)=x(e )+e =e (1x)=0 x=1 . 1. 2. f (0)=0 , f (1)=e =1/e 0.37 , f (2)=2/e 0.27 . So f (1)=1/e is the absolute maximum value and f (0)=0 is the absolute minimum value. 11.

(12) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. ln x / x(1/x)ln x 1ln x = =0 1ln x=0 ln x=1 x=e . f (1)=0/1=0 , , 1,3 . f (x)= 2 2 x x x f (e)=1/e 0.368 , f (3)=(ln 3)/3 0.366 . So f (e)=1/e is the absolute maximum value and f (1)=0 is the absolute minimum value. 60. f (x)=. 3 x3 / = =0 x=3 . f does not exist for x=0 , but 0 is not in the x x domain of f . f (1)=1 , f (3)=33ln 3 0.296 , f (4)=43ln 4 0.159 . So f (1)=1 is the absolute maximum value and f (3)=33ln 3 0.296 is the absolute minimum value. /. 61. f (x)=x3ln x , 1,4 . f (x)=1. x. 2x. x. /. 62. f (x)=e e. 2x. , 0,1 . f (x)=e (1)e. 2. (2)=. 2x. 1. . x. =. 2e. x. x. =0 e =2 x=ln 2 0.69 . f (0)=0. 2x. e e e 1 ln 2 2ln 2 ln 2 1 ln 2 2 1 2 1 1 1 1 2 e = e e =2 2 = = , f (1)=e e 0.233 . So f (ln 2)= , f (ln 2)=e 2 4 4 4 is the absolute maximum value and f (0)=0 is the absolute minimum value.. ( ) ( ). a. b. 63. f (x)=x (1x) , 0 x 1 , a>0 , b>0 . /. b1. a. f (x) =x b(1x) =x. a1. b. (1)+(1x) ax. a1. =x. a1. b1. (1x). x b(1)+(1x) a. b1. (1x). (aaxbx) /. At the endpoints, we have f (0)= f (1)=0 [ the minimum value of f ]. In the interval (0,1) , f (x)=0 a x= . a+b f. So f. a a+b. =. a a+b. a. a a+b. a 1 a+b. b. =. a. a. a. (a+b). a+ba a+b. b. =. a. b. a. a. (a+b). a b. b. b. (a+b). =. ab. ( a+b ). a+b. .. a b. =. ab. ( a+b ). a+b. is the absolute maximum value.. 64.. /. /. We see that f (x)=0 at about x=0.0 and 2.0 , and that f (x) does not exist at about x=0.7 , 1.0 , and 2.7 , so the critical numbers of f are about 0.7 , 0.0 , 1.0 , 2.0 , and 2.7 . 12.

(13) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 65. (a) From the graph, it appears that the absolute maximum value is about f (1.63)=9.71 , and the absolute minimum value is about f (1.63)=7.71 . These values make sense because the graph is symmetric 3. about the point ( 0,1 ) . ( y=x 8x is symmetric about the origin.) 3. /. 2. 8 . 3. /. (b) f (x)=x 8x+1 f (x)=3x 8 . So f (x)=0 x= f. . 8 3. 3. =. . 8 3. =. 16 3. 32 6 8 16 +1=1 or 9 3 3. 8. . 8 3. +1=. 8 3. 8

(14) 8 3. 8 +1 3. 32 6 8 +1=1+ 9 3. (From the graph, we see that the extreme values do not occur at the endpoints.). 66. (a) From the graph, it appears that the absolute maximum value is about f (0.58)=1.47 , and the absolute minimum value is about f (1)= f (0)=1.00 ; that is, at both endpoints. 3. (b) f (x)=e. x x. /. f (x)=e. 3. x x. 3 /9+ 3 /3. and f ( 1/3 ) =e. ( 3x21) . So f /(x)=0 on 2 3 /9. =e. 1,0 x= 1/3 . f (1)= f (0)=1 (minima). (maximum).. 67. (a) From the graph, it appears that the absolute maximum value is about f (0.75)=0.32 , and the absolute minimum value is f (0)= f (1)=0 ; that is, at both endpoints. 13.

(15) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 2. /. (b) f (x)=x xx f (x)=x. 12x. 2. + xx. 2 2 ( x2x ) + ( 2x2x ) = =. 2. 2 xx 3 2 3x4x =0 x(34x)=0 x=0 or . f (0)= f (1)=0 , 4 and f. 3 4. =. 3 4. 3 4. 3 4. 2. =. 2. 2 xx. 2. 3x4x. /. . So f (x)=0 2. 2 xx. 3 3 . 16. 68. (a) From the graph, it appears that the absolute maximum value is about f (5.76)=0.58 , and the absolute minimum value is about f (3.67)=0.58 . cos x / (2+sin x)(sin x)(cos x)(cos x) 12sin x . f (x)= = 2 2 2+sin x ( 2+sin x ) ( 2+sin x ) 3 /2 11 1 7 7 1 / So f (x)=0 sin x= x= or . Now f , = = 3/2 6 2 6 6 3 3 /2 11 1 = = and f . 3/2 6 3 (b) f (x)=. mass 1000 3 = (in g / cm ). But a critical point of will also be a volume V (T ) d 2 dV critical point of V since [ and V is never 0 ], and V is easier to differentiate than =1000V dT dT . 69. The density is defined as =. 2. 3. V (T )=999.870.06426T +0.0085043T 0.0000679T /. 2. V (T )=0.06426+0.0170086T 0.0002037T . Setting this equal to 0 and using the quadratic formula to 2. 0.0170086 0.0170086 4 0.0002037 0.06426. find T , we get T = 3.9665 C or 79.5318 C. 2(0.0002037). Since we are only interested in the region 0 C T 30 C, we check the density at the endpoints 1000 1000. and at 3.9665 C: (0) 1.00013 ; (30) 0.99625 ; 999.87 1003.7628 14.

(16) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. (3.9665). 1000. 1.000255 . So water has its maximum density at about 3.9665 C. 999.7447. W dF ( sin +cos )(0)W ( cos sin ) W ( cos sin ) = = . 2 2 sin +cos d ( sin +cos ) ( sin +cos ) dF sin =0 cos sin =0 = =tan . Substituting tan for in F gives us So d cos (tan )W W tan W tan cos W sin F= = = = =W sin . 2 2 2 (tan )sin +cos 1 sin sin +cos +cos cos W . We compare this with the If tan = , then sin = (see the figure), so F= 2 2 +1 +1 =W . Now because 1 and value of F at the endpoints: F(0)=W and F 2 2 +1 , we have that W 2 2 +1 +1 70. F=. 2. is less than or equal to each of F(0) and F. . Hence,. 2. W is the absolute minimum. +1. value of F( ) , and it occurs when tan = .. 71. We apply the Closed Interval Method to the continuous function 5. 4. 3. 2. I(t)=0.00009045t +0.001438t 0.06561t +0.4598t 0.6270t+99.33 on 0,10 . Its derivative is /. 4. 3. 2. /. I (t)=0.00045225t +0.005752t 0.19683t +0.9196t0.6270 . Since I exists for all t , the only /. critical numbers of I occur when I (t)=0 . We use a rootfinder on a computer algebra system (or a /. graphing device) to find that I (t)=0 when t 29.7186 , 0.8231 , 5.1309 , or 11.0459 , but only the second and third roots lie in the interval 0,10 . The values of I at these critical numbers are I(0.8231) 99.09 and I(5.1309) 100.67 . The values of I at the endpoints of the interval are I(0)=99.33 and I(10) 96.86 . Comparing these four numbers, we see that food was most expensive at t 5.1309 (corresponding roughly to August, 1989) and cheapest at t=10 (midyear 1994). 15.

(17) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. 72. (a) The equation of the graph in the figure is 3. 2. v(t)=0.00146t 0.11553t +24.98169t21.26872 . /. 2. /. /. (b) a(t)=v (t)=0.00438t 0.23106t+24.98169 a (t)=0.00876t0.23106 . a (t)=0 0.23106 t = 26.4 . a(0) 24.98 , a(t ) 21.93 , and a(125) 64.54 . The maximum acceleration is 1 0.00876 1 2. 2. about 64.5 ft / s and the minimum acceleration is about 21.93 ft / s . 2. 2. 3. /. 2. /. 73. (a) v(r)=k(r r)r =kr r kr v (r)=2kr r3kr . v (r)=0 kr(2r 3r)=0 r=0 or 0. 0. 0. 0. 2 r (but 0 3 0. 1 2 1 1 3 r , r , and r , we get v r = kr , 0 2 0 3 0 2 0 8 0 2 4 3 4 1 2 v r = kr , and v(r )=0 . Since > , v attains its maximum value at r= r . This 0 3 0 27 0 27 8 3 0 supports the statement in the text. 4 3 kr . (b) From part (a), the maximum value of v is 27 0 is not in the interval). Evaluating v at. (c) 3. /. 2. /. 74. g(x)=2+(x5) g (x)=3(x5) g (5)=0 , so 5 is a critical number. But g(5)=2 and g takes on values >2 and values <2 in any open interval containing 5 , so g does not have a local maximum or minimum at 5 . 101. 51. /. 100. 50. /. 75. f (x)=x +x +x+1 f (x)=101x +51x +1 1 for all x , so f (x)=0 has no solution. Thus, f (x) has no critical number, so f (x) can have no local maximum or minimum. 76. Suppose that f has a minimum value at c , so f (x) f (c) for all x near c . Then g(x)= f (x) f (c)=g(c) for all x near c , so g(x) has a maximum value at c . /. 77. If f has a local minimum at c , then g(x)= f (x) has a local maximum at c , so g (c)=0 by the case 16.

(18) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.1 Maximum and Minimum Values. /. /. of Fermat’s Theorem proved in the text. Thus, f (c)=g (c)=0 . 78. (a). 3. 2. /. 2. f (x)=ax +bx +cx+d , a 0 . So f (x)=3ax +2bx+c is a quadratic and hence has either 2 , 1 , or 0 real roots, so f (x) has either 2 , 1 or 0 critical numbers. Case (i) (2 critical numbers): 3. f (x)=x 3x /. 2. f (x)=3x 3 , so x=1,1 are critical numbers.. Case (ii) (1 critical number):. Case (iii) (no critical number):. f(x)=x . f (x)=x +3x. 3. /. / 2 f (x)=3x,so x=0 f (x)=3x +3 , is the only critical number. so there are no real roots.. (b) Since there are at most two critical numbers, it can have at most two local extreme values and by (i) this can occur. By (iii) it can have no local extreme value. However, if there is only one critical number, then there is no local extreme value.. 17.

(19) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 2+1. 1+1. x x 3 2 1. f (x)=6x 8x+3 F(x)=6 8 +3x+C=2x 4x +3x+C 2+1 1+1 2 /. 2. 2. Check: F (x)=2 3x 4 2x+3+0=6x 8x+3= f (x) 2. 3. 2. f (x)=4+x 5x F(x)=4x+. 1 3 5 4 x x +C 3 4 3+1. 5+1. 7+1. x x x 1 4 5 6 3 8 +5 3 +C=x x + x x +C 3. f (x)=1x +5x 3x F(x)=x 3+1 5+1 7+1 4 6 8 1 21 4 11 20 10 x + x +8x+C 4. f (x)=x +4x +8 F(x)= 21 11 3. 5. 1/4. 5. f (x)=5x 7x. 7. 3/4. 1/4+1. 1.7. 2. 6. f (x)=2x+3x F(x)=x + 1/2. 6. 1/6. 7. f (x)=6 x x =6x x 1/2+1. 3/4+1. 5/4. 7/4. x x x x 5/4 7/4 F(x)=5 7 +C=5 7 +C=4x 4x +C 1 3 5/4 7/4 +1 +1 4 4 3 2.7 2 10 2.7 x +C=x + x +C 2.7 9. . 1/6+1. 3/2. 7/6. x x x x 3/2 6 7/6 F(x)=6 +C=6 +C=4x x +C 1 1 3/2 7/6 7 +1 +1 2 6 8. f (x)= 9. f (x)=. 4. 3. x +. 10 x. {. 9. 3. 4. 3/4. x =x +x. =10x. 9. 4/3. 7/4. 7/3. x x 4 7/4 3 7/3 F(x)= + +C= x + x +C 7/4 7/3 7 7. has domain ( ,0 ) ( 0, ) , so. 8. 10x 5 +C = +C 1 1 8 8 4x F(x)= 5 +C 2 8 4x See Example 1 for a similar problem.. if x<0. if x>0. 10. 1.

(20) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 3. g(x)=. G(x)=. 54x +2x. {. x. 6. 6. 6. 5. 2. x x 1 2 4 +2x+C = + +2x+C 5 1 1 5 2 5 2 x x 1 2 + +2x+C 2 5 2 x x 4. 11. f (u)=. 3. =5x 4x +2 has domain ( ,0 ) ( 0, ) , so. u +3 u u. 2. =. u. 3/2+1. 3. u. 4 2. +. 3u. 1/2. u. 2. =u +3u. 2. 3/2. if x<0. if x>0. . 1/2. u u 1 3 u 1 3 6 F(u)= +3 +C= u +3 +C= u +C 3 3/2+1 1/2 3 3 u x. x. 2. 12. f (x)=3e +7sec x F(x)=3e +7tan x+C on the interval n. n . ,n + 2 2. .. 13. g( )=cos 5sin G( )=sin 5(cos )+C=sin +5cos +C 14. h( )=. sin . =. 2. cos . 1 sin =sec tan H( )=sec +C on the interval n cos cos 2 1/2. (. 15. f (x)=2x+5 1x. ). =2x+. 5. 2. 2. n . ,n + 2 2. .. 1. F(x)=x +5sin x+C. 1x 2. 16. f (x)=. x +x+1 1 =x+1+ F(x)= x x. 5. {. 1 2 x +x+ln x +C if x<0 1 2 1 2 x +x+ln x +C if x>0 2 2. 6. x x 5 1 6 5 1 6 2 +C=x x +C . F(0)=4 0 0 +C=4 C=4 , so 17. f (x)=5x 2x F(x)=5 5 6 3 3 5 1 6 F(x)=x x +4 . The graph confirms our answer since f (x)=0 when F has a local maximum, f is 3 positive when F is increasing, and f is negative when F is decreasing. 4. 5. 2.

(21) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 2 1. (. 18. f (x)=43 1+x. ). =4. 1. 3 2. F(x)=4x3tan x+C . F(1)=0 43. 1+x. 4. +C=0C=. 3 4 , so 4. 1. 3 4 . Note that f is positive and F is increasing on R . Also, f has smaller 4 values where the slopes of the tangent lines of F are smaller.. F(x)=4x3tan x+. 19. f. / /. 2. 3. x x 2 3 (x)=6x+12x f (x)=6 +12 +C=3x +4x +C 2 3 2. 3. /. 4. x x 3 4 +4 +Cx+D=x +x +Cx+D f (x)=3 3 4 20. f. 21. f 22. f 23. f. 24. f f (t)=. / /. / /. / /. 3. 6. /. (x)=2+x +x f (x)=2x+ (x)=1+x. 4/5. /. f (x)=x+. 1 4 1 7 2 1 5 1 8 x + x +C f (x)=x + x+ x +Cx+D 4 7 20 56. 5 9/5 1 2 5 5 14/5 1 2 25 14/5 x +C f (x)= x + x +Cx+D= x + x +Cx+D 9 2 9 14 2 126. /. (x)=cos x f (x)=sin x+C f (x)=cos x+Cx+D. / / /. (t)=60t f. 2. / /. / / /. (t)=t t f. / /. 3. /. 4. 5. (t)=20t +C f (t)=5t +Ct+D f (t)=t + (t)=. 1 2 Ct +Dt+E 2. 1 2 2 3/2 1 3 4 5/2 / t t +C f (t)= t t +Ct+D 2 3 6 15. 1 4 8 7/2 1 2 t t + Ct +Dt+E 24 105 2 /. 2. 2. 25. f (x)=16x f (x)=x3x +C . f (0)=C and f (0)=8C=8 , so f (x)=x3x +8 . 3.

(22) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. /. 3. 4. 2. 26. f (x)=8x +12x+3 f (x)=2x +6x +3x+C . f (1)=11+C and f (1)=6 4. 2. 11+C=6C=5 , so f (x)=2x +6x +3x5 . /. 1/2. 27. f (x)= x (6+5x)=6x +5x. 3/2. 3/2. 5/2. f (x)=4x +2x +C . 3/2. 5/2. f (1)=6+C and f (1)=10C=4 , so f (x)=4x +2x +4 . /. 4. 4. 3. 2. 28. f (x)=2x3/x =2x3x f (x)=x +x +C because we’re given that x>0 . 2. 3. f (1)=2+C and f (1)=3C=1 , so f (x)=x +1/x +1 . /. 2. 29. f (t)=2cos t+sec t f (t)=2sin t+tan t+C because /2<t< /2 . f =2 ( 3 /2 ) + 3 +C=2 3 +C and f =4C=42 3 , so f (t)=2sin t+tan t+42 3 . 3 3 2. /. 30. f (x)=3x f (x)=. {. 3/x+C. if x>0. 3/x+C. if x<0. 1 2. f (1)=3+C =0C =3 . So f (x)= 2. 2. {. f (1)=3+C =0C =3 , 1. 1. 3/x+3 if x>0 3/x3 if x<0. /. 31. f (x)=2/x f (x)=2ln x +C=2ln (x)+C (since x<0 ). Now f (1)=2ln 1+C=2(0)+C=7C=7 . Therefore, f (x)=2ln (x)+7 , x<0 . 1 1 =4sin 2 2 2 2 1 , so f (x)=4sin x+1 . +C=1C=1 3 3 3 /. 1. 2. 32. f (x)=4/ 1x f (x)=4sin x+C . f. 33. f. / /. 2. /. 3. 2. 1 2. +C=4. /. +C and f 6. 1 2. =1. /. (x)=24x +2x+10 f (x)=8x +x +10x+C . f (1)=8+1+10+C and f (1)=3 19+C=3 1 / 3 2 4 1 3 2 C=22 , so f (x)=8x +x +10x22 and hence, f (x)=2x + x +5x 22x+D . f (1)=2+ +522+D and 3 3 7 59 59 4 1 3 2 , so f (x)=2x + x +5x 22x+ . f (1)=5 D=22 = 3 3 3 3 34. f. / /. 3. /. 2. 4. /. /. (x)=46x40x f (x)=4x3x 10x +C . f (0)=C and f (0)=1C=1 , so. /. 2. 4. 2. 3. 5. f (x)=4x3x 10x +1 and hence, f (x)=2x x 2x +x+D . f (0)=D and f (0)=2 D=2 , so 2. 3. 5. f (x)=2x x 2x +x+2 . 35. 4.

(23) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. f. / /. /. /. /. ( )=sin +cos f ( )=cos +sin +C . f (0)=1+C and f (0)=4C=5 , so. /. f ( )=cos +sin +5 and hence, f ( )=sin cos +5 +D. f (0)=1+D and f (0)=3 D=4 , so f ( )=sin cos +5 +4 . 36. f. / /. (t)=3/ t =3t. hence, f (t)=4t. 1/2. /. f (t)=6t. 1/2. /. /. /. +C . f (4)=12+C and f (4)=7C=5 , so f (t)=6t. 3/2. 5t+D . f (4)=3220+D and f (4)=20 D=8 , so f (t)=4t. / /. /. 2. 2. 1/2. 5 and. 3/2. 5t+8 .. 3. 37. f (x)=212x f (x)=2x6x +C f (x)=x 2x +Cx+D . f (0)=D and f (0)=9 D=9 . f (2)=416+2C+9=2C3 and f (2)=15 2C=18C=9 , so 2. 3. f (x)=x 2x +9x+9 . 38. f. / /. 3. 2. /. 4. 3. 5. 4. 2. (x)=20x +12x +4 f (x)=5x +4x +4x+C f (x)=x +x +2x +Cx+D . f (0)=D and f (0)=8 5. 4. 2. D=8 . f (1)=1+1+2+C+8=C+12 and f (1)=5C=7 , so f (x)=x +x +2x 7x+8 . / /. /. 2. 39. f (x)=2+cos x f (x)=2x+sin x+C f (x)=x cos x+Cx+D . f (0)=1+D and f (0)=1 D=0 . 2 2 f = /4+ C and f =0 C= /4C= , so 2 2 2 2 2 2 f (x)=x cos x x. 2 40. f. / /. t. /. t. t. (t)=2e +3sin t f (t)=2e 3cos t+C f (t)=2e 3sin t+Ct+D . f (0)=2+D and f (0)=0 D=2 . . . 22e . f ( )=2e + C2 and f ( )=0 C=22e C= 2. / /. . 22e t2 . , so f (t)=2e 3sin t+ t. /. 41. f (x)=x , x>0 f (x)=1/x+C f (x)=ln x +Cx+D=ln x+Cx+D (since x>0 ). f (1)=0C+D=0 and f (2)=0 ln 2+2C+D=0 ln 2+2CC=0 [ since D=C ] ln 2+C=0C=ln 2 and D=ln 2 . So f (x)=ln x+(ln 2)xln 2 . 42. f f. / /. / / /. / /. (x)=sin x f. (x)=cos x+C 1= f. /. / /. (0)=1+C C=2 , so. /. /. 2. (x)=cos x+2 f (x)=sin x+2x+D 1= f (0)=D f (x)=sin x+2x+1 f (x)=cos x+x +x+E 2. 1= f (0)=1+E E=0 , so f (x)=cos x+x +x . /. 2. 2. 43. Given f (x)=2x+1 , we have f (x)=x +x+C . Since f passes through ( 1,6 ) , f (1)=6 1 +1+C=6 2. 2. C=4 . Therefore, f (x)=x +x+4 and f (2)=2 +2+4=10 . 5.

(24) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 1 4 / 3 x +C . x+y=0 y=x m=1 . Now m= f (x) 1=x x=1 y=1 (from 4 1 4 the equation of the tangent line), so ( 1,1 ) is a point on the graph of f . From f , 1= (1) +C 4 3 1 4 3 C= . Therefore, the function is f (x)= x + . 4 4 4 /. 3. 44. f (x)=x f (x)=. 45. b is the antiderivative of f . For small x , f is negative, so the graph of its antiderivative must be decreasing. But both a and c are increasing for small x , so only b can be f ’s antiderivative. Also, f is positive where b is increasing, which supports our conclusion. 46. We know right away that c cannot be f ’s antiderivative, since the slope of c is not zero at the x value where f =0 . Now f is positive when a is increasing and negative when a is decreasing, so a is the antiderivative of f . /. 47. The graph of F will have a minimum at 0 and a maximum at 2 , since f =F goes from negative to positive at x=0 , and from positive to negative at x=2 .. 48. The position function is the antiderivative of the velocity function, so its graph has to be horizontal where the velocity function is equal to 0 .. 49.. 6.

(25) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. {. {. 2 if0 x<1 2x+C if0 x<1 f (x)= 1 if1<x<2 f (x)= x+D if1<x<2 f (0)=1 2(0)+C=1C=1 . 1 if2<x 3 x+E if2<x 3 Starting at the point ( 0,1 ) and moving to the right on a line with slope 2 gets us to the point ( 1,1 ) . The slope for 1<x<2 is 1 , so we get to the point ( 2,2 ) . Here we have used the fact that f is continuous. We can include the point x=1 on either the first or the second part of f . The line connecting ( 1,1 ) to ( 2,2 ) is y=x , so D=0 . The slope for 2<x 3 is 1 , so we get to ( 3,1 ) . f (3)=1 3+E=1 E=4 . Thus, /. f (x)=. {. 2x1 if 0 x 1 if 1<x<2 x x+4 if 2 x 3. /. Note that f (x) does not exist at x=1 or at x=2 .. 50. (a) (b) Since F(0)=1 , we can start our graph at ( 0,1 ) . f has a minimum at about x=0.5 , so its derivative is zero there. f is decreasing on ( 0,0.5) , so its derivative is negative and hence, F is CD on ( 0,0.5) /. and has an IP at x 0.5 . On ( 0.5,2.2 ) , f is negative and increasing ( f is positive), so F is decreasing and CU. On ( 2.2, ) , f is positive and increasing, so F is increasing and CU.. 2. (c) f (x)=2x3 x F(x)=x 3. 2 3/2 2 3/2 x +C . F(0)=C and F(0)=1C=1 , so F(x)=x 2x +1 . 3. (d) 7.

(26) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 2. 51. f (x)=sin (x ) , 0 x 4. 4. 52. f (x)=1/(x +1). 53.. 54. 8.

(27) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 55. x 0 0.5 1.0 1.5 2.0 2.5 3.0. f (x) 1 0.959 0.841 0.665 0.455 0.239 0.047. x 3.5 4.0 4.5 5.0 5.5 6.0. f (x) 0.100 0.189 0.217 0.192 0.128 0.047. We compute slopes [values of f (x)=(sin x) / x for 0 < x < 2 ] as in the table. lim f (x)=1. and. +. x 0. draw a direction field as in Example 6. Then we use the direction field to graph F starting at ( 0,0 ). 56. x 0 0.2 0.4 0.6 0.8 1.0 1.2. f (x) 0 0.041 0.169 0.410 0.824 1.557 3.087 9.

(28) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 1.4 1.5. 8.117 21.152. We compute slopes [values of f (x) = x tan x for / 2 < x / 2 ] as in the table and draw a direction field as in Example 6. Then we use the direction field to graph F starting at ( 0,0 ) and extending in both directions. Note that if f is an even function, then the antiderivative F that passes through the origin is an odd function.]. 57.. Remember that the given table values of f are the slopes of F at any x . For example, at x=1.4 , the slope of F is f (1.4)=0 .. 58. (a) (b) The general antiderivative of f (x)=x. 2. is F(x)=. {. 1/x+C. 1. if x<0. since f (x) is not defined if x>0 2 at x=0 . The graph of the general antiderivatives of f (x) looks like the graph in part (a), as expected. 1/x+C. /. 59. v(t)=s (t)=sin tcos t s(t)=cos tsin t+C . s(0)=1+C and s(0)=0C=1 , so s(t)=cos tsin t+1 . /. 60. v(t)=s (t)=1.5 t s(t)=t. 3/2. +C . s(4)=8+C and s(4)=10C=2 , so s(t)=t. 3/2. +2 . 10.

(29) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 1 2 1 2 t 2t+C . v(0)=C and v(0)=3C=3 , so v(t)= t 2t+3 and 2 2 1 3 2 1 3 2 s(t)= t t +3t+D . s(0)=D and s(0)=1 D=1 , and s(t)= t t +3t+1 . 6 6 /. 61. a(t)=v (t)=t2 v(t)=. /. 62. a(t)=v (t)=cos t+sin t v(t)=sin tcos t+C 5=v(0)=1+C C=6 , so v(t)=sin tcos t+6 s(t)=cos tsin t+6t+D 0=s(0)=1+D D=1 , so s(t)=cos tsin t+6t+1 . /. 63. a(t)=v (t)=10sin t+3cos t v(t)=10cos t+3sin t+C s(t)=10sin t3cos t+Ct+D . s(0)=3+D=0 6 6 and s(2 )=3+2 C+D=12 D=3 and C= . Thus, s(t)=10sin t3cos t+ t+3 . 3 2 3 2 1 3 1 4 t t +C s(t)=5t + t t +Ct+D 0=s(0)=D and 2 2 4 2 1 3 1 4 10=s(2)=20+44+2CC=5 , so s(t)=5t+5t + t t . 2 4 /. 2. 64. a(t)=v (t)=10+3t3t v(t)=10t+. 65. (a) We first observe that since the stone is dropped 450 m above the ground, v(0)=0 and s(0)=450 . /. 2. v (t)=a(t)=9.8 v(t)=9.8t+C . Now v(0)=0C=0 , so v(t)=9.8t s(t)=4.9t +D . Last, s(0)=450 2. D=450 s(t)=4504.9t . 2. 2. (b) The stone reaches the ground when s(t)=0 . 4504.9t =0 t =450/4.9 t = 450/4.9 9.58 s. 1. ( ). (c) The velocity with which the stone strikes the ground is v t =9.8 450/4.9 93.9 m / s. 1. (d) This is just reworking parts (a) and (b) with v(0)=5 . Using v(t)=9.8t+C , v(0)=5 0+C=5 2. 2. v(t)=9.8t5 . So s(t)=4.9t 5t+D and s(0)=450 D=450 s(t)=4.9t 5t+450 . Solving s(t)=0 by using the quadratic formula gives us t= ( 5 8845 ) / ( 9.8 ) t 9.09 s. 1. /. 66. v (t)=a(t)=a v(t)=at+C and v =v(0)=C v(t)=at+v 0. s(t)=. 0. 1 2 1 2 at +v t+D s =s(0)=D s(t)= at +v t+s 0 0 0 0 2 2 2. /. 67. By Exercise with a=9.8 , s(t)=4.9t +v t+s and v(t)=s ( t ) =9.8t+v . So 0 0 0 2. (. v ( t ) = 9.8t+v. 2. 0. 22. 2. 2. 0. 0. 2. 2. ) = ( 9.8) t 19.6v t+v =v +96.04t 19.6v t=v 19.6 0. 0. 0. 2. 2. 4.9t +v t 0. 2. is just s(t) without the s term; that is, s(t)s . Thus, v ( t ) =v 19.6 s ( t ) s 0. 0. 0. 0. 2. . But 4.9t +v t 0. . 11.

(30) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 2. 68. For the first ball, s (t)=16t +48t+432 from Example 8. For the second ball, a(t)=32 1. 2. v(t)=32t+C , but v(1)=32(1)+C=24C=56 , so v(t)=32t+56 s(t)=16t +56t+D , but 2. 2. s(1)=16(1) +56(1)+D=432 D=392 , and s (t)=16t +56t+392 . The balls pass each other when 2. 2. 2. s (t)=s (t) 16t +48t+432=16t +56t+392

(31) 8t=40

(32) t=5 s. 1. 2. 2. 2. Another solution: From Exercise , we have s (t)=16t +48t+432 and s (t)=16t +24t+432 . We now 1. 2. 2. 2. want to solve s (t)=s (t1) 16t +48t+432=16(t1) +24(t1)+432 48t=32t16+24t24 40=8t 1. t=5 s.. 2. 69. Using Exercise with a=32 , v =0 , and s =h (the height of the cliff ), we know that the height at 0. 2. 0. /. time t is s(t)=16t +h . v(t)=s (t)=32t and v(t)=120 32t=120 t=3.75 , so 2. 2. 0=s(3.75)=16(3.75) +h h=16(3.75) =225 ft. 70. (a) EIy. / /. =mg(Lx)+. 1 1 2 / 2 1 3 g(Lx) EIy = mg(Lx) g(Lx) +C 2 2 6. 1 3 1 4 / mg(Lx) + g(Lx) +Cx+D . Since the left end of the board is fixed, we must have y=y =0 6 24 1 1 2 1 3 3 1 4 when x=0 . Thus, 0= mgL gL +C and 0= mgL + gL +D . It follows that 2 6 6 24 1 1 1 3 1 4 2 1 3 3 1 4 EIy= mg(Lx) + g(Lx) + mgL + gL x mgL + gL and 6 24 2 6 6 24 1 1 1 1 3 1 4 2 1 3 3 1 4 f (x)=y= mg(Lx) + g(Lx) + mgL + gL x mgL + gL 6 EI 24 2 6 6 24 (b) f (L)<0 , so the end of the board is a distance approximately f (L) below the horizontal. From our result in (a), we calculate EIy=. f (L) =. 1 EI. 1 = EI. 1 3 1 4 1 3 1 4 mgL + gL mgL gL 2 6 6 24 3. m L + 3 8. 1 gL 3 1 4 mgL + gL = 3 EI 8. Note: This is positive because g is negative. /. 2. 71. Marginal cost =1.920.002x=C (x)C(x)=1.92x0.001x +K . But C(1)=1.920.001+K=562 2. K=560.081 . Therefore, C(x)=1.92x0.001x +560.081C(100)=742.081 , so the cost of producing 12.

(33) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 100 items is $742.08 . dm 1/2 1/2 =x m(x)=2x +C dx and m(0)=C=0 , so m(x)=2 x . Thus, the mass of the 100centimeter rod is m(100)=2 100 =20 g. 72. Let the mass, measured from one end, be m(x) . Then m(0)=0 and =. 73. Taking the upward direction to be positive we have that for 0 t 10 (using the subscript 1 to /. 2. refer to 0 t 10 ), a (t)= ( 90.9t ) =v (t) v (t)=9t+0.45t +v , but v (0)=v =10 1. 1. 1. 0. 1. 0. 9 2 3 v (t)=9t+0.45t 10=s (t) s (t)= t +0.15t 10t+s . But s (0)=500=s 1 1 1 0 1 0 2 9 2 3 s (t)= t +0.15t 10t+500 . s (10)=450+150100+500=100 , so it takes more than 10 seconds for 1 1 2 2. /. /. 2. the raindrop to fall. Now for t>10 , a(t)=0=v (t) v(t)= constant =v (10)=9(10)+0.45(10) 10=55 1. v(t)=55 . At 55 ft / s, it will take 100/55 1.8 s to fall the last 100 ft. Hence, the total time is 100 130 10+ = 11.8 s. 55 11 50 5280 220 220 = ft / s, so v(t)=22t+ . The 3600 3 3 220 10 2 220 = t , the distance covered is car stops when v(t)=0

(34) t= . Since s(t)=11t + 3 22 3 3 10 2 220 10 1100 10 =11 + = =122.2 ft. s 3 3 3 9 3 /. 74. v (t)=a(t)=22 . The initial velocity is 50 mi / h =. 75. a(t)=k , the initial velocity is 30 mi / h =30 . 5280 =44 ft / s, and the final velocity (after 5 3600. 5280 220 = ft / s . So v(t)=kt+C and v(0)=44C=44 . Thus, v(t)=kt+44 3600 3 220 220 88 88 2 v(5)=5k+44 . But v(5)= 5k= k= 5.87 ft / s . , so 5k+44= 3 3 3 15 seconds) is 50 mi / h =50 . 76. a(t)=16 v(t)=16t+v where v is the car’s speed (in ft / s) when the brakes were applied. The 0. 0. 1 1 2 2 v . Now s(t)= (16)t +v t=8t +v t . The car travels 200 ft in the 0 0 0 16 0 2 2 1 1 1 2 1 v =200 200=8 v +v v = v time that it takes to stop, so s 0 16 0 16 0 32 0 16 0 car stops when 16t+v =0

(35) t=. 2. v =32 200=6400 v =80 ft / s ( 54.54 mi / h). 0. 0. 13.

(36) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. 2. 77. Let the acceleration be a(t)=k km / h . We have v(0)=100 km / h and we can take the initial position s(0) to be 0 . We want the time t for which v(t)=0 to satisfy s(t)<0.08 km. In general, f. /. /. v (t)=a(t)=k , so v(t)=kt+C , where C=v(0)=100 . Now s (t)=v(t)=kt+100 , so s(t)=. 1 2 kt +100t+D , 2. 1 2 kt +100t . Since v(t )=0 , we have kt +100=0 or t =100/k , so f f f 2 2 1 100 100 1 1 5,000 +100 =10 , 000 = s(t )= k . The condition s(t ) must f f 2 k k 2k k k 5,000 5,000 2 <0.08 >k [ k is negative] k<62 , 500 km / h , or equivalently, satisfy is k 0.08 3125 2 k< 4.82 m / s . 648 where D=s(0)=0 . Thus, s(t)=. 2. 2. 3. 78. (a) For 0 t 3 we have a(t)=60t v(t)=30t +C v(0)=0=C v(t)=30t , so s(t)=10t +C 3. s(0)=0=C s(t)=10t . Note that v(3)=270 and s(3)=270 . For 3<t 17 : a(t)=g=32 ft / s v(t)=32(t3)+C v(3)=270=C v(t)=32(t3)+270 2. 2. s(t)=16(t3) +270(t3)+C s(3)=270=C s(t)=16(t3) +270(t3)+270 . Note that v(17)=178 and s(17)=914 . For 17<t 22 : The velocity increases linearly from 178 ft / s to 18 ft / s during this period, so v 18 ( 178 ) 160 2 = = =32 . Thus, v(t)=32(t17)178 s(t)=16(t17) 178(t17)+914 and t 2217 5 s(22)=424 ft. For t>22 : v(t)=18 s(t)=18(t22)+C . But s(22)=424=C s(t)=18(t22)+424 . Therefore, until the rocket lands, we have. v(t)= and. s(t)=. {. { 10t. 2. 30t 32 ( t3) +270 32(t17)178 18. 3. if if if if. 0 t 3 3<t 17 17<t 22 t>22. if 0 t 3 2. 16(t3) +270(t3)+270. if 3<t 17. 16(t17) 178 ( t17) +914 18(t22)+424. if 17<t 22 if t>22. 2. 14.

(37) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.10 Antiderivatives. (b) To find the maximum height, set v(t) on 3<t 17 equal to 0 . 32(t3)+270=0 t =11.4375 s and 1. ( ). ( ). 2. ( ). the maximum height is s t =16 t 3 +270 t 3 +270=1409.0625 ft. 1. 1. 1. (c) To find the time to land, set s(t)=18(t22)+424=0 . Then t22=. 424 =23.5 , so t 45.6 s. 18. 5280 2 ft / s =132 ft / s. Then a(t)=4 ft / s v(t)=4t+C , but 3600 132 v(0)=0C=0 . Now 4t=132 when t= =33 s, so it takes 33 s to reach 132 ft / s. Therefore, taking 4 79. (a) First note that 90 mi / h =90. 2. s(0)=0 , we have s(t)=2t , 0 t 33 . So s(33)=2178 ft. 15 minutes =15(60)=900 s, so for 33<t 933 we have v(t)=132 ft / s s(933)=132(900)+2178=120 , 978 ft =22.9125 mi. (b) As in part (a), the train accelerates for 33 s and travels 2178 ft while doing so. Similarly, it decelerates for 33 s and travels 2178 ft at the end of its trip. During the remaining 90066=834 s it travels at 132 ft / s, so the distance traveled is 132 834=110 , 088 ft. Thus, the total distance is 2178+110 , 088+2178=114 , 444 ft =21.675 mi. (c) 45 mi =45(5280)=237 , 600 ft. Subtract 2(2178) to take care of the speeding up and slowing down, and we have 233 , 244 ft at 132 ft / s for a trip of 233 , 244/132=1767 s at 90 mi / h. The total time is 1767+2(33)=1833s=30 min 33s=30.55 min. (d) 37.5(60)=2250 s. 22502(33)=2184 s at maximum speed. 2184(132)+2(2178)=292 , 644 total feet or 292 , 644/5280=55.425 mi.. 15.

(38) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 2. 1. f (x)=x 4x+1 , 0,4 . Since f is a polynomial, it is continuous and differentiable on R , so it is /. continuous on 0,4 and differentiable on ( 0,4 ) . Also, f (0)=1= f (4) . f (c)=02c4=0c=2 , which is in the open interval ( 0,4 ) , so c=2 satisfies the conclusion of Rolle’s Theorem. 3. 2. 2. f (x)=x 3x +2x+5 , 0,2 . f is continuous on 0,2 and differentiable on ( 0,2 ) . Also, 6 3624 1 / 2 f (0)=5= f (2) . f (c)=0 3c 6c+2=0c= =1 3 , both in ( 0,2 ) . 6 3 3. f (x)=sin 2 x , 1,1 . f , being the composite of the sine function and the polynomial 2 x , is continuous and differentiable on R , so it is continuous on 1,1 and differentiable on ( 1,1 ) . Also, 1 / f (1)=0= f (1) . f (c)=02 cos 2 c=0cos 2 c=02 c= +2 nc= +n . If n=0 or 1 , 2 4 1 3 then c= , is in ( 1,1 ) . 4 4 4. f (x)=x x+6 , 6,0 . f is continuous on its domain, 6, ) , and differentiable on ( 6, ) , so it 3c+12 / is continuous on 6,0 and differentiable on ( 6,0 ) . Also, f (6)=0= f (0) . f (c)=0 =0 2 c+6 c=4 , which is in ( 6,0 ) . 2 1/3 2/3 2/3 / / 5. f (x)=1x . f (1)=1(1) =11=0= f (1) . f (x)= x , so f (c)=0 has no solution. This 3 /. does not contradict Rolle’s Theorem, since f (0) does not exist, and so f is not differentiable on ( 1,1 ) . 2. 2. 2. /. 3. /. 6. f (x)=(x1) . f (0)=(01) =1=(21) = f (2) . f (x)=2(x1) f (x) is never 0 . This does not /. contradict Rolle’s Theorem since f (1) does not exist. f (8) f (0) 64 1 1 / = = . The values of c which satisfy f (c)= seem to be about c=0.8 , 3.2 , 4.4 , 80 8 4 4 and 6.1 . 7.. f (7) f (1) 25 1 1 / = = . The values of c which satisfy f (c)= seem to be about c=1.1 , 2.8 , 71 6 2 2 4.6 , and 5.8 .. 8.. 1.

(39) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 9. (a), 8.55 1 9 (b) The equation of the secant line is y5= 81 (x1) y= 2 x+ 2 .. (c). /. 2. f (x)=x+4/x f (x)=14/x . 1 4 / 2 =3 2 . Thus, an equation of the tangent So f (c)= c =8 c=2 2 , and f (c)=2 2 + 2 2 2 1 1 line is y3 2 = ( x2 2 ) y= x+2 2 . 2 2. 10. (a) It seems that the tangent lines are parallel to the secant at x 1.2 . 3. /. 2. (b) The slope of the secant line is 2 , and its equation is y=2x . f (x)=x 2x f (x)=3x 2 , 2 3 / 2 1.155 . Our estimates were off by about 0.045 in each so we solve f (c)=2 3c =4 c= 3 case. 2. 11. f (x)=3x +2x+5 , 1,1 . f is continuous on 1,1 and differentiable on ( 1,1 ) since f (b) f (a) / polynomials are continuous and differentiable on R . f (c)= ba 2.

(40) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 6c+2=. f (1) f (1) 106 = =26c=0c=0 , which is in ( 1,1 ) . 1(1) 2 3. /. 12. f (x)=x +x1 , 0,2 . f is continuous on 0,2 and differentiable on ( 0,2 ) . f (c)= 2. 3c +1=. f (2) f (0) 20. 2 9(1) 2 2 2 4 3c =51c = c= , but only is in ( 0,2 ) . 2 3 3 3 2x. 13. f (x)=e. , 0,3 . f is continuous and differentiable on R , so it is continuous on 0,3 and 6. 0. 6. f (b) f (a) 2c e e 2c 1e 2e = e = differentiable on ( 0,3) . f (c)= 30 6 ba /. 1 c= ln 2. 6. 2c=ln. 6. 1e 6. 1e 6. . 0.897 , which is in ( 0,3) .. x f (b) f (a) / , 1,4 . f is continuous on 1,4 and differentiable on ( 1,4 ) . f (c)= x+2 ba 2 1 3 3 2 2 = (c+2) =18c=2 3 2 . 2+3 2 2.24 is in ( 1,4 ) . 2 41 (c+2). 14. f (x)=. /. /. 15. f (x)= x1 . f (3) f (0)= 31 01 =1 . Since f (c)=1 if c<1 and f (c)=1 if c>1 , /. f (c)(30)= 3 and so is never equal to 1 . This does not contradict the Mean Value Theorem since /. f (1) does not exist. x+1 / / 1(x1)1(x+1) 2 16. f (x)= . f (2) f (0)=3(1)=4 . f (x)= . Since f (x)<0 for all x = 2 2 x1 (x1) (x1) /. (except x=1 ), f (c)(20) is always <0 and hence cannot equal 4 . This does not contradict the Mean Value Theorem since f is not continuous at x=1 . 3. 5. 17. Let f (x)=1+2x+x +4x . Then f (1)=6<0 and f (0)=1>0. Since f is a polynomial, it is continuous, so the Intermediate Value Theorem says that there is a number c between 1 and 0 such that f (c)=0. Thus, the given equation has a real root. Suppose the equation has distinct real roots a and b with a<b . Then f (a)= f (b)=0 . Since f is a polynomial, it is differentiable on ( a,b) and /. continuous on a,b . By Rolle’s Theorem, there is a number r in ( a,b) such that f (r)=0 . But /. 2. 4. /. f (x)=2+3x +20x 2 for all x , so f (x) can never be 0 . This contradiction shows that the equation can’t have two distinct real roots. Hence, it has exactly one real root. 3.

(41) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 18. Let f (x)=2x1sin x . Then f (0)=1<0 and f ( /2)= 2>0 . f is the sum of the polynomial 2x1 and the scalar multiple ( 1 ) sin x of the trigonometric function sin x , so f is continuous (and differentiable) for all x . By the Intermediate Value Theorem, there is a number c in ( 0, /2 ) such that f (c)=0 . Thus, the given equation has at least one real root. If the equation has distinct real roots a and b with a<b , then f (a)= f (b)=0 . Since f is continuous on a,b and differentiable on ( a,b) , /. /. Rolle’s Theorem implies that there is a number r in ( a,b) such that f (r)=0 . But f (r)=2cos r >0 since cos r 1 . This contradiction shows that the given equation can’t have two distinct real roots, so it has exactly one real root. 3. 19. Let f (x)=x 15x+c for x in 2,2 . If f has two real roots a and b in 2,2 , with a<b , then f (a)= f (b)=0 . Since the polynomial f is continuous on a,b and differentiable on ( a,b) , Rolle’s /. /. 2. Theorem implies that there is a number r in ( a,b) such that f (r)=0 . Now f (r)=3r 15 . Since r is 2. in ( a,b) , which is contained in 2,2 , we have r <2 , so r <4 . It follows that 2. /. 3r 15<3 415=3<0 . This contradicts f (r)=0 , so the given equation can’t have two real roots in 2,2 . Hence, it has at most one real root in 2,2 . 4. 20. f (x)=x +4x+c . Suppose that f (x)=0 has three distinct real roots a , b , d where a<b<d . Then f (a)= f (b)= f (d)=0 . By Rolle’s Theorem there are numbers c and c with a<c <b and b<c <d and 1. 0= f. /. /. ( c ) = f ( c ) , so f 1. /. /. 2. (. 3. 1. 2. (x)=0 must have at least two real solutions. However. ). 3. 2. (. ). 2. 0= f (x)=4x +4=4 x +1 =4 ( x+1 ) x x+1 has as its only real solution x=1 . Thus, f (x) can have at most two real roots. 21. (a) Suppose that a cubic polynomial P(x) has roots a <a <a <a , so 1. 2. 3. 4. ( ) ( ) ( ) ( ) . By Rolle’s Theorem there are numbers c , c , c with a <c <a a <c <a and a <c <a and P ( c ) =P ( c ) =P ( c ) =0 . Thus, the seconddegree polynomial. P a =P a =P a =P a 1. 2. 3. 4. 1. /. 2. 2. 3. 3. 3. /. 3. 1. 1. 2. ,. /. 1. 4. 2. 2. 3. /. P (x) has three distinct real roots, which is impossible. (b) We prove by induction that a polynomial of degree n has at most n real roots. This is certainly true for n=1 . Suppose that the result is true for all polynomials of degree n and let P(x) be a polynomial of degree n+1 . Suppose that P(x) has more than n+1 real roots, say a <a <a <. <a <a . Then P a =P a =. =P a =0 . By Rolle’s Theorem 1. 2. 3. n+1. ( ) ( ). n+2. 1. there are real numbers c ,. ,c. n+1. 1. P. /. ( ). c =. =P 1. /. 2. with a <c <a ,. ,a 1. 1. 2. ( ) n+2. <c. n+1. ( c ) =0 Thus, the n th degree polynomial P n+1. <a. n+1 /. n+2. and. (x) has at least n+1 roots. This. contradiction shows that P(x) has at most n+1 real roots.. 4.

(42) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 22. (a) Suppose that f (a)= f (b)=0 where a<b . By Rolle’s Theorem applied to f on a,b there is a /. number c such that a<c<b and f (c)=0 . (b) Suppose that f (a)= f (b)= f (c)=0 where a<b<c . By Rolle’s Theorem applied to f (x) on a,b and /. /. b,c there are numbers a<d<b and b<e<c with f (d)=0 and f (e)=0 . By Rolle’s Theorem applied /. to f (x) on d,e there is a number g with d<g<e such that f. / /. (g)=0 .. (c) Suppose that f is n times differentiable on R and has n+1 distinct real roots. Then f least one real root.. ( n). has at. /. 23. By the Mean Value Theorem, f (4) f (1)= f (c)(41) for some c

(43) ( 1,4 ) . But for every c

(44) ( 1,4 ) /. /. we have f (c) 2 . Putting f (c) 2 into the above equation and substituting f (1)=10 , we get /. /. f (4)= f (1)+ f (c)(41)=10+3 f (c) 10+3 2=16 . So the smallest possible value of f (4) is 16 . /. /. 24. If 3 f (x) 5 for all x , then by the Mean Value Theorem, f (8) f (2)= f (c) ( 82 ) for some c in 2,8 . ( f is differentiable for all x , so, in particular, f is differentiable on ( 2,8 ) and continuous on 2,8 . /. Thus, the hypotheses of the Mean Value Theorem are satisfied.) Since f (8) f (2)=6 f (c) and /. /. 3 f (c) 5 , it follows that 6 3 6 f (c) 6 5 18 f (8) f (2) 30. 25. Suppose that such a function f exists. By the Mean Value Theorem there is a number 0<c<2 with f (2) f (0) 5 5 / / f (c)= = . But this is impossible since f (x) 2< for all x , so no such function can 20 2 2 exist. 26. Let h= f g . Then since f and g are continuous on a,b and differentiable on ( a,b) , so is h , and thus h satisfies the assumptions of the Mean Value Theorem. Therefore, there is a number c with /. /. /. a<c<b such that h(b)=h(b)h(a)=h (c)(ba) . Since h (c)<0 , h (c)(ba)<0 , so f (b)g(b)=h(b)<0 and hence f (b)<g(b) . 1 x , and a=0 . Notice that f (0)=1=g(0) and 2 1 1 1 / / f (x)= < =g (x) for x>0 . So by Exercise 26, f (b)<g(b) 1+b <1+ b for b>0 . 2 2 1+x 2 1 Another method: Apply the Mean Value Theorem directly to either f (x)=1+ x 1+x or g(x)= 1+x 2 on 0,b . 27. We use Exercise 26 with f (x)= 1+x , g(x)=1+. 5.

(45) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. 28. f satisfies the conditions for the Mean Value Theorem, so we use this theorem on the interval f (b) f (b) / b,b : = f (c) for some c

(46) ( b,b) . But since f is odd, f (b)= f (b) . Substituting this b(b) f (b)+ f (b) f (b) / / = f (c) = f (c) . into the above equation, we get 2b b 29. Let f (x)=sin x and let b<a . Then f (x) is continuous on b,a and differentiable on ( b,a ) . By the Mean Value Theorem, there is a number c

(47) ( b,a ) with /. sin asin b= f (a) f (b)= f (c)(ab)=(cos c)(ab) . Thus, sin asin b cos c ba ab . If a<b , then sin asin b = sin bsin a ba = ab . If a=b , both sides of the inequality are 0 . /. /. 30. Suppose that f (x)=c . Let g(x)=cx , so g (x)=c . Then, by Corollary 7, f (x)=g(x)+d , where d is a constant, so f (x)=cx+d . /. /. /. /. 2. /. /. 2. 31. For x>0 , f (x)=g(x) , so f (x)=g (x) . For x<0 , f (x)=(1/x) =1/x and g (x)=(1+1/x) =1/x , /. /. so again f (x)=g (x) . However, the domain of g(x) is not an interval so we cannot conclude that f g is constant (in fact it is not). 1. 1. (. 2. ). 32. Let f (x)=2sin xcos 12x . Then / / 2 4x 2 4x f (x)= = =0 (since x 0 ). Thus, f (x)=0 for 2 2 2 2 2 1x 1x 2x 1x 1 12x all x

(48) ( 0,1 ) . Thus, f (x)=C on ( 0,1 ) . To find C , let x=0.5 . Thus, 1 1 2sin (0.5)cos (0.5)=2 =0=C . We conclude that f (x)=0 for x in ( 0,1 ) . By continuity 6 3. (. ). 1. of f , f (x)=0 on 0,1 . Therefore, we see that f (x)=2sin xcos 1. 2sin x=cos. 1. /. ( 12x2) =0. ( 12x2) .. 33. Let f (x)=arcsin f (x)=. 1. 1. x1 x+1. . Note that the domain of f is 0, ) . Thus, 2 1 1 1 ( x+1 ) ( x1 ) 2 . = =0 . Then 2 1+x 2 x x x (x+1) (x+1) ( x+1 ) 2arctan x +. x1 2 1 x+1 f (x)=C on ( 0, ) by Theorem 5. By continuity of f , f (x)=C on 0, ) . To find C , we let x=0 x1 . arcsin(1)2arctan(0)+ =C 0+ =0=C . Thus, f (x)=0 arcsin =2arctan x 2 2 2 x+1 2 34. Let v(t) be the velocity of the car t hours after 2:00 P.M. Then 6.

(49) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.2 The Mean Value Theorem. v(1/6)v(0) 5030 1 = =120 . By the Mean Value Theorem, there is a number c such that 0<c< with 1/60 1/6 6 /. /. v (c)=120 . Since v (t) is the acceleration at time t , the acceleration c hours after 2:00 P.M. is 2. exactly 120 mi / h . 35. Let g(t) and h(t) be the position functions of the two runners and let f (t)=g(t)h(t) . By hypothesis, f (0)=g(0)h(0)=0 and f (b)=g(b)h(b)=0 , where b is the finishing time. Then by the f (b) f (0) / Mean Value Theorem, there is a time c , with 0<c<b , such that f (c)= . But f (b)= f (0)=0 b0 /. /. /. /. /. /. , so f (c)=0 . Since f (c)=g (c)h (c)=0 , we have g (c)=h (c) . So at time c , both runners have /. /. the same speed g (c)=h (c) . /. 36. Assume that f is differentiable (and hence continuous) on R and that f (x) 1 for all x . Suppose f has more than one fixed point. Then there are numbers a and b such that a<b , f (a)=a , and f (b)=b . Applying the Mean Value Theorem to the function f on a,b , we find that there is a number c in f (b) f (a) ba / / . But then f (c)= =1 , contradicting our assumption that ( a,b) such that f (c)= ba ba /. f (x) 1 for every real number x . This shows that our supposition was wrong, that is, that f cannot have more than one fixed point.. 7.

(50) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. 1. (a) f is increasing on ( 0,6 ) and ( 8,9 ) . (b) f is decreasing on ( 6,8 ) . (c) f is concave upward on ( 2,4 ) and ( 7,9 ) . (d) f is concave downward on ( 0,2 ) and ( 4,7) . (e) The points of inflection are ( 2,3) , ( 4,4.5) and ( 7,4 ) (where the concavity changes). 2. (a) f is increasing on ( 1, 3.8 ) and ( 5, 6.5) . (b) f is decreasing on ( 0,1 ) , ( 3.8,5) , ( 6.5,8 ) , and ( 8,9 ) . (c) f is concave upward on ( 0,3) and ( 8,9 ) . (d) f is concave downward on ( 3,5) and ( 5,8 ) . (e) The point of inflection is ( 3, 1.8 ) (where the concavity changes). 3. (a) Use the Increasing/Decreasing (I/D) Test. (b) Use the Concavity Test. (c) At any value of x where the concavity changes, we have an inflection point at ( x,f(x) ) . 4. (a) See the First Derivative Test. (b) See the Second Derivative Test and the note that precedes Example 7. /. /. 5. (a) Since f (x)>0 on ( 1,5) , f is increasing on this interval. Since f (x)<0 on ( 0,1 ) and ( 5,6 ) , f is decreasing on these intervals. /. (b) Since f (x)=0 at x=1 and f. /. changes from negative to positive there, f changes from decreasing /. /. to increasing and has a local minimum at x=1 . Since f (x)=0 at x=5 and f changes from positive to negative there, f changes from increasing to decreasing and has a local maximum at x=5 . /. /. 6. (a) f (x)>0 and f is increasing on ( 0,1 ) and ( 3,5) . f (x)<0 and f is decreasing on ( 1,3) and ( 5,6 ) . /. (b) Since f (x)=0 at x=1 and x=5 and f. /. changes from positive to negative at both values, f /. changes from increasing to decreasing and has local maxima at x=1 and x=5 . Since f (x)=0 at x=3 /. and f changes from negative to positive there, f changes from decreasing to increasing and has a local minimum at x=3 . / /. 7. There is an inflection point at x=1 because f (x) changes from negative to positive there, and so the graph of f changes from concave downward to concave upward. There is an inflection point at / /. x=7 because f (x) changes from positive to negative there, and so the graph of f changes from concave upward to concave downward. 8. (a) f is increasing on the intervals where 1.

(51) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. /. f (x)>0 , namely, ( 2,4 ) and ( 6,9 ) . (b) f has a local maximum where it changes from increasing to decreasing, that is, where f changes from positive to negative (at x=4 ). Similarly, where f has a local minimum (at x=2 and at x=6 ). (c) When f. /. is increasing, its derivative f. / /. /. /. changes from negative to positive, f. is positive and hence, f is concave upward. This /. happens on ( 1,3) , ( 5,7) , and ( 8,9 ) . Similarly, f is concave downward when f is decreasing that is, on ( 0,1 ) , ( 3,5) , and ( 7,8 ) . (d) f has inflection points at x=1 , 3 , 5 , 7 , and 8 , since the direction of concavity changes at each of these values. 9. The function must be always decreasing and concave downward.. 10. (a) The rate of increase of the population is initially very small, then gets larger until it reaches a maximum at about t=8 hours, and decreases toward 0 as the population begins to level off. (b) The rate of increase has its maximum value at t=8 hours. (c) The population function is concave upward on ( 0,8 ) and concave downward on ( 8,18 ) . (d) At t=8 , the population is about 350 , so the inflection point is about ( 8,350 ) . 3. /. 2. 11. (a) f (x)=x 12x+1 f (x)=3x 12=3(x+2)(x2) . /. We don’t need to include "3" in the chart to determine the sign of f (x) . Interval. x+2. x2. x<2 2<x<2 x>2. + +. +. /. f (x) + +. f increasing on ( ,2) decreasing on (2,2) increasing on (2, ). So f is increasing on ( ,2 ) and ( 2, ) and f is decreasing on ( 2,2 ) . (b) f changes from increasing to decreasing at x=2 and from decreasing to increasing at x=2 . Thus, f (2)=17 is a local maximum value and f (2)=15 is a local minimum value. (c) f. / /. (x)=6x . f. / /. (x)>0 x>0 and f. / /. (x)<0 x<0 . Thus, f is concave upward on ( 0, ) and 2.

(52) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. concave downward on ( ,0 ) . There is an inflection point where the concavity changes, at ( 0,f(0) ) = ( 0,1 ) . 2. 3. /. 2. /. /. 12. (a) f (x)=53x +x f (x)=6x+3x =3x(x2) . Thus, f (x)>0 x<0 or x>2 and f (x)<0 0<x<2 . So f is increasing on ( ,0 ) and ( 2, ) and f is decreasing on ( 0,2 ) . (b) f changes from increasing to decreasing at x=0 and from decreasing to increasing at x=2 . Thus, f (0)=5 is a local maximum value and f (2)=1 is a local minimum value. / /. / /. / /. (c) f (x)=6+6x=6(x1) . f (x)>0 x>1 and f (x)<0 x<1 . Thus, f is concave upward on ( 1, ) and concave downward on ( ,1 ) . There is an inflection point at ( 1,3) . 4. 2. /. (. 3. ). 2. 13. (a) f (x)=x 2x +3 f (x)=4x 4x=4x x 1 =4x ( x+1 ) ( x1 ) . Interval. x+1. x. x1. x<1 1<x<0 0<x<1 x>1. + + +. + +. +. /. f decreasing on ( ,1) increasing on (1,0) decreasing on (0,1) increasing on (1, ). f (x) + +. So f is increasing on (1,0) and (1, ) and f is decreasing on ( ,1) and (0,1) . (b) f changes from increasing to decreasing at x=0 and from decreasing to increasing at x=1 and x=1 . Thus, f (0)=3 is a local maximum value and f ( 1)=2 are local minimum values. / / 2 2 1 / / (c) f (x)=12x 4=12 x =12 ( x+1/ 3 ) ( x1/ 3 ) . f (x)>0 x<1/ 3 or x>1/ 3 and 3 f. / /. (x)<01/ 3 <x<1/ 3 . Thus, f is concave upward on ( , 3 /3) and. 3 /3, ) and 22 . 3 /3, 9. concave downward on ( 3 /3, 3 /3) . There are inflection points at 2. 14. (a) f (x)=. x. f. 2. x +3. /. 2 2 ( x +3) (2x)x (2x) 6x (x)= = 2 ( x2+3) ( x2+3) 2. /. /. (. . The denominator is positive so the sign /. of f (x) is determined by the sign of x . Thus, f (x)>0 x>0 and f (x)<0 x<0 . So f is increasing on ( 0, ) and f is decreasing on ( ,0 ) . (b) f changes from decreasing to increasing at x=0 . Thus, f (0)=0 is a local minimum value. (c) 2. f. / /. (x) =. 2. (. 2. ). x +3 (6)6x 2 x +3 (2x). ( x +3) 2. 2 2. =. (. 2. 6 x +3. ). 2. 2. x +34x. ( x2+3) 4 3.

(53) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. =. / /. ( 2) = 18(x+1)(x1) ( x2+3) 3 ( x2+3) 3. 6 33x. .. / /. (x)<0 x<1 or x>1 . Thus, f is concave upward on ( 1,1 ) and 1 concave downward on ( ,1 ) and ( 1, ) . There are inflection points at 1, . 4 f. (x)>01<x<1 and f. 1 5 <x< 2 3 3 7 5 1 7 5 / or or . So f is increasing on <x<3 . f (x)<0cos x> 0<x< <x< , 3 3 2 3 3 3 3 7 5 7 and and . ,3 , and f is decreasing on 0, , 3 3 3 3 5 (b) f changes from increasing to decreasing at x= , and from decreasing to increasing at x= 3 3 7 5 5 and at x= . Thus, f = + 3 6.97 is a local maximum value and 3 3 3 7 7 f = 3 0.68 and f = 3 5.60 are local minimum values. 3 3 3 3 /. /. 15. (a) f (x)=x2sin x on ( 0,3 ) f (x)=12cos x . f (x)>012cos x>0cos x<. / /. / /. (c) f (x)=2sin x >00<x< and 2 <x<3 , f (x)<0 <x<2 . Thus, f is concave upward on ( 0, ) and ( 2 ,3 ) , and f is concave downward on ( ,2 ) . There are inflection points at ( , ) and ( 2 ,2 ) . 2. /. 16. (a) f (x)=cos x2sin x , 0 x 2 . f (x)=2cos x sin x2cos x=2cos x ( 1+sin x ) . Note that 1+sin x 0 [ since sin x 1 ], with equality sin x=1 x=3 /2 [ since 0 x 2 ] cos x=0 . /. /. Thus, f (x)>0cos x <0 /2<x<3 /2 and f (x)<0cos x>00<x< /2 or 3 /2<x<2 . Thus, f is increasing on ( /2,3 /2 ) and f is decreasing on ( 0, /2 ) and ( 3 /2,2 ) . (b) f changes from decreasing to increasing at x= /2 and from increasing to decreasing at x=3 /2 . Thus, f ( /2)=2 is a local minimum value and f (3 /2)=2 is a local maximum value. (c) f. / /. 2. (. 2. 2. (x) =2sin x ( 1+sin x ) 2cos x=2sin x+2sin x2 1sin x. ). 2. =4sin x+2sin x2=2(2sin x1)(sin x+1) so f. / /. (x)>0sin x >. 1 5 , and f <x< 2 6 6. / /. 1 and sin x

(54) 10<x< or 2 6 5 and concave downward on , 6 6. (x)<0sin x <. 5 3 3 or <x< <x<2 . Thus, f is concave upward on 6 2 2. 4.

(55) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. , 6 5 1 , 6 4. 5 3 , 6 2. 0,. 3 ,2 2. , and. . There are inflection points at. 1 , 6 4. and. . x. x. /. x. x. /. 17. (a) y= f (x)=xe f (x)=xe +e =e (x+1) . So f (x)>0 x+1>0 x>1 . Thus, f is increasing on ( 1, ) and decreasing on ( ,1 ) . 1. (b) f changes from decreasing to increasing at its only critical number, x=1 . Thus, f (1)=e local minimum value. x. /. x. / /. x. x. is a. / /. (c) f (x)=e (x+1) f (x)=e (1)+(x+1)e =e (x+2) . So f (x)>0 x+2>0 x>2 . Thus, f is concave upward on ( 2, ) and concave downward on ( ,2 ) . Since the concavity changes 2. (. direction at x=2 , the point 2,2e 2 x. 2 x. /. ) is an inflection point. x. x. /. 18. (a) y= f (x)=x e f (x)=x e +2xe =x(x+2)e . So f (x)>0 x(x+2)>0 either x<2 or x>0 . Therefore f is increasing on ( ,2 ) and ( 0, ) , and decreasing on ( 2,0 ) . 2. (b) f changes from increasing to decreasing at x=2 , so f (2)=4e is a local maximum value. f changes from decreasing to increasing at x=0 , so f (0)=0 is a local minimum value. /. (. 2. ). x. (c) f (x)= x +2x e f. / /. (. 2. ). x. x. (x)= x +2x e +e (2x+2)=e. x. ( x2+4x+2) . f / /(x)=0 x2+4x+2=0. / /. x=2 2 . f (x)<02 2 <x<2+ 2 , so f is concave downward on ( 2 2 ,2+ 2 ) and concave upward on ( ,2 2 ) and ( 2+ 2 , ) . There are inflection points at ( 2 2 ,f ( 2 2 ) ) ( 3.41,0.38 ) and ( 2+ 2 ,f ( 2+ 2 ) ) ( 0.59,0.19 ) . ln x . (Note that f is only defined for x>0 .) x 1 ln x 1 1/2 x (1/x)ln x x x 2 x 2 x 2ln x 2 / 2 =. = >02ln x>0 ln x<2 x<e . f (x)= 3/2 x x 2 x 2x. 19. (a) y= f (x)=. ( 2) and decreasing on ( e2, ) . 2 2 2 2 ln e f changes from increasing to decreasing at x=e , so f ( e ) = = e. Therefore f is increasing on 0,e (b). is a local maximum. 2. e. value. (c). 5.

(56) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. (. 3/2. / /. f. (x) =. ( 2x3/2) 2 x (2+3ln x6) 4x. f. / /. (x)=0ln x=. 3. ) = 2x1/2+3x1/2(ln x2) 4x. 1/2. =. 1/2. 2x (1/x)(2ln x) 3x. =. 3. 3ln x8 4x. 8 8/3 x=e . f 3. 5/2. / /. 8/3. (x)>0 x>e. 8/3. , so f is concave upward on (e , ) and concave. 8/3. 8/3. e ,. downward on (0,e ) . There is an inflection point at. 8 4/3 e ( 14.39,0.70 ) . 3. 20. (a) y= f (x)=xln x . (Note that f is only defined for x>0 .) /. 1. /. f (x)=x(1/x)+ln x=1+ln x . f (x)>0ln x+1>0ln x>1 x>e . Therefore f is increasing on ( 1/e, ) and decreasing on ( 0,1/e ) . (b) f changes from decreasing to increasing at x=1/e , so f (1/e)=1/e is a local minimum value. (c) f. / /. (x)=1/x>0 for x>0 . So f is concave upward on its entire domain, and has no inflection point. 5. /. (. 4. 2. ). 21. f (x)=x 5x+3 f (x)=5x 5=5 x +1 (x+1)(x1) . /. /. First Derivative Test: f (x)<0 1<x<1 and f (x)>0 x>1 or x<1 . Since f positive to negative at x=1 , f (1)=7 is a local maximum value; and since f to positive at x=1 , f (1)=1 is a local minimum value. Second Derivative Test: f. / /. 3. /. (x)=20x . f (x)=0 x= 1 . f. / /. /. /. changes from. changes from negative. (1)=20<0 f (1)=7 is a local. / /. maximum value. f (1)=20>0 f (1)=1 is a local minimum value. Preference: For this function, the two tests are equally easy. 22. f (x)=. x 2. f. /. 2 ( x +4) 1x(2x) (x)= = 2. x +4. x +4. 2. 2. 4x () 2. 2. =. (2+x)(2x). ( x +4) 2. 2. .. x +4 /. /. /. First Derivative Test: f (x)>0 2<x<2 and f (x)<0 x>2 or x<2 . Since f changes from 1 / positive to negative at x=2 , f (2)= is a local maximum value; and since f changes from negative 4 1 to positive at x=2 , f (2)= is a local minimum value. Second Derivative Test: 4. 6.

(57) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. 2. 2. / /. f. (. 2. ) (. ). 2. x +4 (2x) 4x 2 x +4 (2x). (x) =. 2. ( x2+4) 2 2 2 2 2x ( x +4) ( x +4) +2 ( 4x ) ( x2+4) 4. = /. f (x)=0 x= 2 . f. / /. (2)=. =. (. 2. 2x 12x. ). ( x2+4) 3. 1 1 >0 f (2)= is a local minimum value. 16 4. 1 1 <0 f (2)= is a local maximum value. 16 4 Preference: Since calculating the second derivative is fairly difficult, the First Derivative Test is easier to use for this function. f. / /. (2)=. 1 1 1/2 (1x) (1)=1 . Note that f is defined for 1x 0 ; that is, 2 2 1x 1 1 3 / / for x 1 . f (x)=0 2 1x =1 1x = 1x= x= . f does not exist at x=1 , but we 2 4 4 can’t have a local maximum or minimum at an endpoint. 3 3 / / / First Derivative Test: f (x)>0 x< and f (x)<0 <x<1 . Since f changes from positive to 4 4 3 3 5 = is a local maximum value. negative at x= , f 4 4 4 3 1 1 / / 3/2 / / 1 (1x) (1)= =2<0 Second Derivative Test: f (x)= .f 3 4 2 2 4 ( 1x ) 3 5 f = is a local maximum value. 4 4 Preference: The First Derivative Test may be slightly easier to apply in this case. /. 23. f (x)=x+ 1x f (x)=1+. 4. 3. /. 4. 2. 3. 3. 3. 2. 3. 2. 24. (a) f (x)=x (x1) f (x)=x 3(x1) +(x1) 4x =x (x1) 3x+4(x1) =x (x1) (7x4) 4 The critical numbers are 0 , 1 , and . 7 (b) f. / /. 2. 2. 3. 3. 2. (x) =3x (x1) (7x4)+x 2(x1)(7x4)+x (x1) 7 2. =x (x1) 3(x1)(7x4)+2x(7x4)+7x(x1) Now f. / /. (0)= f. / /. (1)=0 , so the Second Derivative Test gives no information for x=0 or x=1 . 7.

(58) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. f. 4 7. / /. =. 2. 4 7. 4 1 7. 0+0+7. there is a local minimum at x= (c) f. /. 4 7. 4 1 7. =. 4 7. 2. . 3 7. (4). . 3 7. >0 , so. 4 . 7. is positive on ( ,0 ) , negative on. 0,. 4 7. 4 ,1 7. , positive on. , and positive on ( 1, ) .. 4 , and no local maximum or minimum at 7. So f has a local maximum at x=0 , a local minimum at x= x=1 . /. 25. (a) By the Second Derivative Test, if f (2)=0 and f .. / /. (2)=5<0 , f has a local maximum at x=2. /. / /. (b) If f (6)=0 , we know that f has a horizontal tangent at x=6 . Knowing that f (6)=0 does not provide any additional information since the Second Derivative Test fails. For example, the first and 4. 4. 3. second derivatives of y= ( x6 ) , y= ( x6 ) , and y= ( x6 ) all equal zero for x=6 , but the first has a local minimum at x=6 , the second has a local maximum at x=6 , and the third has an inflection point at x=6 . /. 26. f (x)>0 for all x

(59) 1 with vertical asymptote x=1 , so f is increasing on ( ,1 ) and ( 1, ) . / /. / /. f (x)>0 if x<1 or x>3 , and f (x)<0 if 1<x<3 , so f is concave upward on ( ,1 ) and ( 3, ) , and concave downward on ( 1,3) . There is an inflection point when x=3 .. /. /. /. /. 27. f (0)= f (2)= f (4)=0 horizontal tangents at x=0 , 2 , 4 . f (x)>0 if x<0 or 2<x<4 f is /. increasing on ( ,0 ) and ( 2,4 ) . f (x)<0 if 0<x<2 or x>4 f is decreasing on ( 0,2 ) and ( 4, ) . / /. / /. f (x)>0 if 1<x<3 f is concave upward on ( 1,3) . f (x)<0 if x<1 or x>3 f is concave downward on ( ,1 ) and ( 3, ) . There are inflection points when x=1 and 3 .. 8.

(60) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. 28.. /. /. /. f (1)= f (1)=0 horizontal tangents at x= 1 . f (x)<0 if x <1 f is decreasing on ( 1,1 ) . /. /. f (x)>0 if 1< x <2 f is increasing on ( 2,1 ) and ( 1,2 ) . f (x)=1 if x >2 the graph of f has constant slope 1 on ( ,2 ) and ( 2, ) . f . Inflection point ( 0,1 ) .. / /. (x)<0 if 2<x<0 f is concave downward on ( 2,0 ). /. /. 29. f (x)>0 if x <2 f is increasing on ( 2,2 ) . f (x)<0 if x >2 f is decreasing on ( ,2 ) /. and ( 2, ) . f (2)=0 horizontal tangent at x=2 . lim x 2. asymptote or vertical tangent (cusp) at x=2 . f ( 2, ) .. / /. /. f (x) = there is a vertical. (x)>0 if x

(61) 2 f is concave upward on ( ,2 ) and. 30.. /. /. f (x)>0 if x <2 f is increasing on ( 2,2 ) . f (x)<0 if x >2 f is decreasing on ( ,2 ) and /. ( 2, ) . f (2)=0 , so f has a horizontal tangent (and local maximum) at x=2 . lim f (x)=1 y=1 is a x . horizontal asymptote. f (x)= f (x) f is an odd function (its graph is symmetric about the origin). Finally, f. / /. (x)<0 if 0<x<3 and f. 31. (a) f is increasing where f where f. /. /. / /. (x)>0 if x>3 , so f is CD on ( 0,3) and CU on ( 3, ) .. is positive, that is, on ( 0,2 ) , ( 4,6 ) , and ( 8, ) ; and decreasing. is negative, that is, on ( 2,4 ) and ( 6,8 ) .. (b) f has local maxima where f minima where f. /. /. changes from positive to negative, at x=2 and at x=6 , and local. changes from negative to positive, at x=4 and at x=8 . 9.

(62) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. (c) f is concave upward (CU) where f. /. is increasing, that is, on ( 3,6 ) and ( 6, ) , and concave. /. downward (CD) where f is decreasing, that is, on ( 0,3) . (d) There is a point of in.ection where f changes from being CD to being CU, that is, at x = 3.. (e) /. 32. (a) f is increasing where f negative, on ( 0,1 ) and ( 6,8 ) .. is positive, on ( 1,6 ) and ( 8, ) , and decreasing where f. (b) f has a local maximum where f where f. /. /. /. is. changes from positive to negative, at x=6 , and local minima. changes from negative to positive, at x=1 and at x=8 .. (c) f is concave upward where f. /. is increasing, that is, on ( 0 2 ) , ( 3, 5) ; and ( 7, ) and. /. concave downward where f is decreasing, that is, on ( 2 3) , ( 5, 7) . (d) There are points of inflection where f changes its direction of concavity, at x=2 , x=3 , x=5 and x=7 .. (e) 3. 2. /. 2. (. 2. ). /. 33. (a) f (x)=2x 3x 12x f (x)=6x 6x12=6 x x2 =6(x2)(x+1) . f (x)>0 x<1 or x>2 /. and f (x)<01<x<2 . So f is increasing on ( ,1 ) and ( 2, ) , and f is decreasing on ( 1,2 ) . (b) Since f changes from increasing to decreasing at x=1 , f (1)=7 is a local maximum value. Since f changes from decreasing to increasing at x=2 , f (2)=20 is a local minimum value. 1 1 / / / / / / (c) f (x)=6(2x1) f (x)>0 on . So f is concave , and f (x)<0 on , 2 2 1 1 upward on . There is a change in concavity at , and concave downward on , 2 2 1 13 1 . x= , and we have an inflection point at , 2 2 2 (d) 10.

(63) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. 3. /. (. 2. ). 2. /. /. 34. (a) f (x)=2+3xx f (x)=33x =3 x 1 =3(x+1)(x1) . f (x)>01<x<1 and f (x)<0 x<1 or x>1 . So f is increasing on ( 1,1 ) and f is decreasing on ( ,1 ) and ( 1, ) . (b) f (1)=0 is a local minimum value and f (1)=4 is a local maximum value. / / / / / / (c) f (x)=6x f (x)>0 on ( ,0 ) and f (x)<0 on ( 0, ) . So f is concave upward on ( ,0 ) and concave downward on ( 0, ) . There is an inflection point at ( 0,2 ) . (d). 4. 2. /. (. 3. ). 2. 35. (a) f (x)=x 6x f (x)=4x 12x=4x x 3 =0 when x=0 , 3 . Interval. 4x. | x< 3. 2. /. f. . x 3 +. f (x) . decreasing on ( , 3 ). 3 <x<0. . . +. increasing on ( 3,0 ). 0<x< 3. +. . . decreasing on ( 0, 3 ). x> 3. +. +. +. increasing on. (. 3, ). (b) Local minimum values f ( 3 ) =9 , local maximum value f (0)=0 / /. 2. (. 2. ). 2. (c) f (x)=12x 12=12 x 1 >0 x >1 x >1 x>1 or x<1 , so f is CU on ( ,1 ) , ( 1, ) and CD on ( 1,1 ) . Inflection points at ( 1,5) (d). 11.

(64) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. 3. 4. /. 2. 3. 2. /. 36. (a) g(x)=200+8x +x g (x)=24x +4x =4x (6+x)=0 when x=6 and when x=0 . g (x)>0 x>6 /. ( x

(65) 0 ) and g (x)<0 x<6 , so g is decreasing on ( ,6 ) and g is increasing on ( 6, ) , with a horizontal tangent at x=0 . (b) g(6)=232 is a local minimum value. There is no local maximum value. (c) g. / /. 2. (x)=48x+12x =12x(4+x)=0 when x=4 and when x=0 . g. / /. (x)>0 x<4 or x>0 and. / /. g (x)<04<x<0 , so g is CU on ( ,4 ) and ( 0, ) , and g is CD on ( 4,0 ) . Inflection points at ( 4,56 ) and ( 0,200 ). (d) 5. 3. /. 4. 2. 2. 37. (a) h(x)=3x 5x +3 h (x)=15x 15x =15x /. ( x21) =0 when x=0 , 1 . Since 15x2 is. 2. nonnegative, h (x)>0 x >1 x >1 x>1 or x<1 , so h is increasing on ( ,1 ) and ( 1, ) and decreasing on ( 1,1 ) , with a horizontal tangent at x=0 . (b) Local maximum value h(1)=5 , local minimum value h(1)=1 (c) h. h. / /. / /. (. 3. 2. ). (x) =60x 30x=30x 2x 1 1 1 =60x x+ x 2 2. 1 1 1 1 or <x<0 , so h is CU on ,0 and , 2 2 2 2 1 1 7 and 0, . Inflection points at ( 0,3) and ,3 2 8 2 2. (x)>0 when x>. ,. 1 2. . and CD on .. (d) 12.

(66) Stewart Calculus ET 5e 0534393217;4. Applications of Differentiation; 4.3 How Derivatives Affect the Shape of a Graph. (. 2. )3. (. /. 2. )2. 38. (a) h(x)= x 1 h (x)=6x x 1 0 x>0 ( x

(67) 1 ), so h is increasing on ( 0, ) and decreasing on ( ,0 ) . (b) h(0)=1 is a local minimum value. 2 1 / / 2 2 2 2 2 (c) h (x)=6 x 1 +24x x 1 =6 x 1 5x 1 . The roots 1 and divide R into five 5 intervals.. (. ). (. ) (. Interval. x +. x<1 1 5. 1<x<. . 1 1 <x< 5 5 1 <x<1 5 x>1 +. . 2. )(. ). 2. 1 5. and. 1 ,1 5. Concavity. h +. +. . downward. . +. upward. +. . downward. +. +. upward. From the table, we see that h is CU on ( ,1 ) , 1,. / /. 5x 1 +. . ( x). 1 1 , 5 5. . Inflection points at ( 1,0 ) and. upward. and ( 1, ) , and CD on . 1 64 , 5 125. (d) /. 39. (a) A(x)=x x+3 A (x)=x /. 1 x x+2(x+3) 3x+6 1/2 . (x+3) + x+3 1= + x+3 = = 2 2 x+3 2 x+3 2 x+3 /. The domain of A is 3, ) . A (x)>0 for x>2 and A (x)<0 for 3<x<2 , so A is increasing on 13.