Thomas' Calculus 13th Edition

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

Chapter 7: Transcendental Functions - Practice Exercises - Page 439: 45

Answer

$$ - \frac{1}{2}{\left( {\ln x} \right)^{ - 2}} + C $$

Work Step by Step

$$\eqalign{ & \int {\frac{{{{\left( {\ln x} \right)}^{ - 3}}}}{x}} dx \cr & {\text{integrate by the substitution method}} \cr & {\text{set }}u = \ln x{\text{ then }}\frac{{du}}{{dx}} = \frac{1}{x},\,\,\,\,dx = xdu \cr & {\text{write the integrand in terms of }}u \cr & \int {\frac{{{{\left( {\ln x} \right)}^{ - 3}}}}{x}} dx = \int {\frac{{{u^{ - 3}}}}{x}} \left( {xdu} \right) \cr & {\text{cancel common terms}} \cr & = \int {{u^{ - 3}}} du \cr & {\text{integrating}}{\text{,}} \cr & = \frac{{{u^{ - 2}}}}{{ - 2}} + C \cr & = - \frac{1}{2}{u^{ - 2}} + C \cr & {\text{replace }}\ln x{\text{ for }}u \cr & = - \frac{1}{2}{\left( {\ln x} \right)^{ - 2}} + C \cr} $$
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