Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 8 - Techniques of Integration - 8.1 Integration by Parts - Exercises - Page 396: 76

Answer

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

Work Step by Step

Given $$\int \frac{(\ln x)^{2} d x}{x^{2}}$$ Let $$u =\ln x\ \ \ \ \ \ du =\frac{1}{x}dx $$ Then $$\int \frac{(\ln x)^{2} d x}{x^{2}}= \int u^{2} e^{-u} d u $$ Use $$\int x^{n} e^{-x} d x=-x^{n} e^{-x}+n \int x^{n-1} e^{-x} d x $$ Then \begin{aligned} \int u^{2} e^{-u} d u &=-u^{2} e^{-u}+2 \int u^{2-1} e^{-u} d u \\ &=-u^{2} e^{-u}+2 \int u e^{-u} d u \\ &=-u^{2} e^{-u}-2 u e^{-u}+2 \int e^{-u} d u \\ &=-u^{2} e^{-u}-2 u e^{-u}-2 e^{-u}+C \\ &=-\frac{(\ln x)^{2}}{x}-2 \frac{\ln x}{x}-2 \frac{1}{x}+C \end{aligned}
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