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 - Section 8.1 - Using Basic Integration Formulas - Exercises 8.1 - Page 448: 17

Answer

$$\frac{1}{8}\ln \left( {1 + 4{{\ln }^2}y} \right) + C$$

Work Step by Step

$$\eqalign{ & \int {\frac{{\ln y}}{{y + 4y{{\ln }^2}y}}} dy \cr & {\text{Factoring the denomiantor}}{\text{, the GCF is }}y \cr & = \int {\frac{{\ln y}}{{y\left( {1 + 4{{\ln }^2}y} \right)}}} dy \cr & {\text{Integrate by the substitution method}}{\text{,}} \cr & \,\,{\text{Let }}u = 1 + 4{\ln ^2}y,\,\,\,du = 0 + 8\ln y\left( {\frac{1}{y}} \right)dy,\,\,\,\,dy = \frac{{ydu}}{{8\ln y}} \cr & \,\,{\text{Write the integrand in terms of }}u \cr & \int {\frac{{\ln y}}{{y\left( {1 + 4{{\ln }^2}y} \right)}}} dy = \int {\frac{{\ln y}}{{y\left( u \right)}}} \left( {\frac{{ydu}}{{8\ln y}}} \right) \cr & = \int {\frac{1}{{\left( u \right)}}} \left( {\frac{{du}}{8}} \right) \cr & = \frac{1}{8}\int {\frac{1}{u}} du \cr & {\text{Integrating}} \cr & = \frac{1}{8}\ln \left| u \right| + C \cr & {\text{Write in terms of }}y,{\text{ substitute }}1 + 4{\ln ^2}y{\text{ for }}y \cr & = \frac{1}{8}\ln \left| {1 + 4{{\ln }^2}y} \right| + C \cr & = \frac{1}{8}\ln \left( {1 + 4{{\ln }^2}y} \right) + C \cr} $$
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