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 - 7.2 Integration By Parts - Exercises Set 7.2 - Page 498: 30

Answer

$$\frac{3}{{2\sqrt e }} - \frac{2}{e}$$

Work Step by Step

$$\eqalign{ & \int_{\sqrt e }^e {\frac{{\ln x}}{{{x^2}}}} dx \cr & \int_{\sqrt e }^e {{x^{ - 2}}\ln x} dx \cr & {\text{substitute }}u = \ln x,{\text{ }}du = \frac{1}{x}dx \cr & dv = {x^{ - 2}}dx,{\text{ }}v = \frac{{{x^{ - 1}}}}{{ - 1}} \cr & {\text{applying integration by parts}}{\text{, we have}} \cr & \int_{\sqrt e }^e {{x^{ - 2}}\ln x} dx = \left. {\left( {\frac{{{x^{ - 1}}}}{{ - 1}}\ln x} \right)} \right|_{\sqrt e }^e - \int_{\sqrt e }^e {\left( {\frac{{{x^{ - 1}}}}{{ - 1}}} \right)\left( {\frac{1}{x}dx} \right)} \cr & \int_{\sqrt e }^e {{x^{ - 2}}\ln x} dx = \left. {\left( { - \frac{{\ln x}}{x}} \right)} \right|_{\sqrt e }^e + \int_{\sqrt e }^e {\frac{1}{{{x^2}}}} dx \cr & {\text{integrating}} \cr & \int_{\sqrt e }^e {{x^{ - 2}}\ln x} dx = \left. {\left( { - \frac{{\ln x}}{x}} \right)} \right|_{\sqrt e }^e - \left. {\left( {\frac{1}{x}} \right)} \right|_{\sqrt e }^e \cr & \int_{\sqrt e }^e {{x^{ - 2}}\ln x} dx = \left. {\left( { - \frac{{\ln x + 1}}{x}} \right)} \right|_{\sqrt e }^e \cr & {\text{evaluate limits}} \cr & = \left( { - \frac{{\ln e + 1}}{e}} \right) + \left( {\frac{{\ln \sqrt e + 1}}{{\sqrt e }}} \right) \cr & {\text{simplify}} \cr & = - \frac{2}{e} + \frac{{3/2}}{{\sqrt e }} \cr & = \frac{3}{{2\sqrt e }} - \frac{2}{e} \cr} $$
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