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Thomas Calculus 13th [Solutions]

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Section 4.5 Indeterminate Forms and LHôpitals Rule 283<br />

40.<br />

3 1 1<br />

(3 1)(sin ) 3sin (3 1)(cos ) 1 3cos 3cos (3 1)( sin )<br />

lim x<br />

x x x x x x x x x x<br />

lim lim lim<br />

x sin x xsin x sin x x cos x cos x cos x xsin<br />

x<br />

x 0 x 0 x 0 x 0<br />

3 3 (1)(0) 6<br />

1 1 0 2<br />

3<br />

41.<br />

1<br />

ln x ( x 1) 1<br />

x<br />

1 x<br />

1 ln ( 1)(ln ) 1<br />

(ln x) ( x 1)<br />

( ln ) 1<br />

x<br />

lim 1 1 lim lim lim<br />

x x x x x x x<br />

x 1 x 1 x 1 x 1<br />

lim<br />

x 1<br />

1 1 1<br />

(ln x 1) 1 (0 1) 1 2<br />

42.<br />

1 cos<br />

(1 cos x) (sin x)(cos x)<br />

lim (csc x cot x cos x) lim x cos x lim<br />

sin x sin x sin x<br />

x 0 x 0 x 0<br />

2 2<br />

lim sin x cos x sin x 0 1 0<br />

cos x<br />

1<br />

1<br />

x 0<br />

43. lim cos 1 lim sin lim cos 1<br />

0 e 1 0 e 1 0 e<br />

h h h<br />

e<br />

44. (1 h<br />

lim ) lim e 1 lim e 1<br />

2<br />

h 0 h h 0<br />

2h<br />

h 0<br />

2 2<br />

45.<br />

t 2<br />

t t t<br />

lim e t lim e 2t lim e 2 lim e 1<br />

t t t t<br />

t e 1 t e t e t e<br />

46.<br />

2<br />

2 x<br />

lim x e lim x lim 2x<br />

lim 2 0<br />

x x x<br />

x x e x e x e<br />

lim x sin x 1 cos sin 0<br />

tan lim x lim x<br />

0<br />

x x<br />

0 sec tan 0 2 sec tan 2sec 2<br />

0<br />

x x x x x x x x x x<br />

47.<br />

2 2 2<br />

48.<br />

x 2<br />

x x<br />

lim e 1 2 1<br />

2 2<br />

2 2 4 2 2<br />

sin lim e e<br />

0 0<br />

cos sin lim x x<br />

0<br />

cos sin lim x x<br />

e e e e<br />

x x x x x x x x<br />

0<br />

xsin x 2cos x 2<br />

1<br />

x x x x<br />

49.<br />

2 2 2<br />

lim sin cos 1 sin cos 2sin<br />

2<br />

tan lim lim lim 2cos 2<br />

2 2<br />

0 0 sec 1 0 tan 0<br />

50.<br />

2<br />

lim sin 3x 3x x lim 3cos3x 3 2x lim 3cos3x 3 2x lim<br />

9sin 3x<br />

2<br />

x 0<br />

sin xsin 2x x 0<br />

2sin x cos 2x cos xsin 2x x 0<br />

sin x cos 2x sin 3x x 0<br />

2sin xsin 2x cos xcos 2x 3cos3x<br />

2 1<br />

4 2<br />

1/(1 ) 1/(1 )<br />

51. The limit leads to the indeterminate form 1 . Let ( ) x ln ( ) ln x<br />

f x x f x x ln x<br />

1 x<br />

. Now<br />

lim ln f ( x ) lim ln x<br />

1 x<br />

lim 1<br />

1. Therefore<br />

x 1 x 1 x 1<br />

1<br />

x<br />

1/(1 x) ln f ( x) 1<br />

lim x lim f ( x) lim e e 1<br />

e<br />

x 1 x 1 x 1<br />

Copyright<br />

2014 Pearson Education, Inc.

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