Calculus: Early Transcendentals (2nd Edition)

Published by Pearson
ISBN 10: 0321947347
ISBN 13: 978-0-32194-734-5

Chapter 7 - Integration Techniques - 7.5 Partial Fractions - 7.5 Exercises - Page 550: 54

Answer

$$Area = 2 + \frac{4}{9}\ln \left( {\frac{8}{{17}}} \right) + \ln \left( {\frac{2}{5}} \right)$$

Work Step by Step

$$\eqalign{ & \frac{1}{x} = \frac{x}{{3x + 4}} \cr & {\text{solve for }}x \cr & 3x + 4 = {x^2} \cr & {x^2} - 3x - 4 = 0 \cr & \left( {x - 4} \right)\left( {x + 1} \right) = 0 \cr & x = 4,{\text{ }}x = - 1,{\text{ and the line }}x = 10 \cr & {\text{the interval is }}\left[ {4,10} \right] \cr & \frac{x}{{3x + 4}} \geqslant \frac{1}{x}{\text{ in the interval }}\left[ {4,10} \right] \cr & {\text{the area of the region is}} \cr & Area = \int_4^{10} {\left( {\frac{x}{{3x + 4}} - \frac{1}{x}} \right)} dx \cr & {\text{use long division for }}\frac{x}{{3x + 4}} \cr & Area = \int_4^{10} {\left( {\frac{1}{3} - \frac{{4/3}}{{3x + 4}} - \frac{1}{x}} \right)} dx \cr & {\text{integrating}} \cr & Area = \left( {\frac{1}{3}x - \frac{4}{9}\ln \left| {3x + 4} \right| - \ln \left| x \right|} \right)_4^{10} \cr & {\text{evaluate limits}} \cr & Area = \left( {\frac{1}{3}\left( {10} \right) - \frac{4}{9}\ln \left| {3\left( {10} \right) + 4} \right| - \ln \left| {10} \right|} \right) - \left( {\frac{1}{3}\left( 4 \right) - \frac{4}{9}\ln \left| {3\left( 4 \right) + 4} \right| - \ln \left| 4 \right|} \right) \cr & Area = \frac{{10}}{3} - \frac{4}{9}\ln \left| {\left( {34} \right)} \right| - \ln \left( {10} \right) - \frac{4}{3} + \frac{4}{9}\ln \left( {16} \right) + \ln \left( 4 \right) \cr & {\text{properties of logarithms}} \cr & Area = 2 + \frac{4}{9}\ln \left( {\frac{8}{{17}}} \right) + \ln \left( {\frac{2}{5}} \right) \cr} $$
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