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Section 3.5 Exponential and Logarithmic Models 247<br />

39.<br />

pt <br />

1000<br />

(a)<br />

(b)<br />

1 9e 0.1656t 1000<br />

p5 <br />

animals<br />

1 9e0.16565 203<br />

(c)<br />

500 <br />

1 9e 0.1656 t 2<br />

9e 0.1656t 1<br />

e 0.1656t 1 9<br />

1000<br />

1 9e 0.1656t<br />

t ln19<br />

0.1656 13<br />

months<br />

1300<br />

0 100<br />

0<br />

The horizontal asymptotes are p 0 and<br />

p 1000. The population will approach 1000<br />

as time increases.<br />

40.<br />

y <br />

663<br />

© Houghton Mifflin Company. All rights reserved.<br />

1 72e 0.547t, 0 ≤ t ≤ 18<br />

(a) 1000<br />

(b) For t 19, y 662.<br />

For t 30, y 663.<br />

(c) As t →, y → 663 limiting value.<br />

0<br />

18<br />

0<br />

1 663,<br />

(d) Answers will vary.<br />

41. R log 10 I<br />

I 0<br />

log 10I ⇒ I 10 R<br />

42. R log 10 I<br />

I 0<br />

log 10I<br />

(a) I 10 6.1 1,258,925<br />

(a) R log 10 39,811,000 7.6<br />

(b) I 10 7.6 39,810,717<br />

(b) R log 10 12,589,000 7.1<br />

(c) I 10 9.0 1,000,000,000<br />

(c) R log 10 251,200 5.4<br />

43. I 10 log 10 II 0 , where I 0 10 12 watt per square meter.<br />

(a) 10 10 10 log 10 1010<br />

12 10 10 log 10 102 20 decibels<br />

(b) 10 5 10 log 10 105<br />

12 10 10 log 10 10 7 70 decibels<br />

(c) 10 0 10 log 10 100<br />

12 10 10 log 10 1012 120 decibels<br />

44.<br />

I 0<br />

10 log I<br />

10 12 10<br />

10 log 10 I<br />

(a) 10 4 10 log 10 104<br />

12 decibels<br />

10 10 log 1010 8 80<br />

(b) 10 3 90 decibels<br />

(c) 10 2 100 decibels

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