Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 7 - Principles Of Integral Evaluation - 7.5 Integrating Rational Functions By Partial Fractions - Exercises Set 7.5 - Page 522: 42

Answer

$$2\ln \left| {1 + \ln x} \right| - \frac{3}{{1 + \ln x}} + C$$

Work Step by Step

$$\eqalign{ & {\text{Let }}u = \ln x,{\text{ }}du = \frac{1}{x}dx \cr & \int {\frac{{5 + 2\ln x}}{{x{{\left( {1 + \ln x} \right)}^2}}}dx = } \int {\frac{{5 + 2u}}{{{{\left( {1 + u} \right)}^2}}}du} \cr & {\text{Decompose }}\frac{{5 + 2u}}{{{{\left( {1 + u} \right)}^2}}}{\text{ into partial fractions}} \cr & \frac{{5 + 2u}}{{{{\left( {1 + u} \right)}^2}}} = \frac{A}{{1 + u}} + \frac{B}{{{{\left( {1 + u} \right)}^2}}} \cr & 5 + 2u = A\left( {1 + u} \right) + B \cr & 5 + 2u = A + Au + B \cr & 2u + 5 = Au + B + A \cr & A = 2,{\text{ }}B = 3 \cr & \frac{{5 + 2u}}{{{{\left( {1 + u} \right)}^2}}} = \frac{2}{{1 + u}} + \frac{3}{{{{\left( {1 + u} \right)}^2}}} \cr & {\text{Rewrite the integrand}} \cr & \int {\frac{{5 + 2u}}{{{{\left( {1 + u} \right)}^2}}}du} = \int {\left( {\frac{2}{{1 + u}} + \frac{3}{{{{\left( {1 + u} \right)}^2}}}} \right)du} \cr & = \int {\frac{2}{{1 + u}}} du + \int {\frac{3}{{{{\left( {1 + u} \right)}^2}}}du} \cr & {\text{Integrating}} \cr & = 2\ln \left| {1 + u} \right| - \frac{3}{{1 + u}} + C \cr & {\text{Write in terms of }}x,{\text{ replace }}u = \ln x \cr & = 2\ln \left| {1 + \ln x} \right| - \frac{3}{{1 + \ln x}} + C \cr} $$
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