Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 8: Techniques of Integration - Practice Exercises - Page 519: 107

Answer

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

Work Step by Step

$$\eqalign{ & \int {\frac{{\ln x}}{{x + x\ln x}}} dx \cr & {\text{Factor the denominator}} \cr & \int {\frac{{\ln x}}{{x + x\ln x}}} dx = \int {\frac{{\ln x}}{{\left( {1 + \ln x} \right)x}}} dx \cr & \cr & {\text{Integrate by using the substitution method}}{\text{,}} \cr & {\text{Let }}u = 1 + \ln x,\,\,\,\ln x = u - 1,\,\,\,\,\frac{1}{x}dx = du \cr & {\text{Write the integrand in terms of }}u \cr & \,\,\int {\frac{{\ln x}}{{\left( {1 + \ln x} \right)x}}} dx = \int {\frac{{u - 1}}{u}} du \cr & = \int {\left( {1 - \frac{1}{u}} \right)} du \cr & {\text{Integrate}} \cr & = u - \ln \left| u \right| + C \cr & {\text{Write in terms of }}x,{\text{ substitute }}1 + \ln x{\text{ for }}u \cr & = 1 + \ln x - \ln \left| {1 + \ln x} \right| + C \cr & {\text{Combine the constants}} \cr & = \ln x - \ln \left| {1 + \ln x} \right| + C \cr} $$
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