Calculus (3rd Edition)

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

Chapter 8 - Techniques of Integration - 8.3 Trigonometric Substitution - Exercises - Page 410: 10

Answer

$\frac{1}{48}tan^{-1}(\frac{3}{2})+\frac{1}{104}$

Work Step by Step

let $x$ = $\frac{2}{3}tanθ$ $dx$ = $\frac{2}{3}sec^{2}θdθ$ and $4+9x^{2}$ = $4+9(\frac{2}{3}tanθ)^{2}$ = $4+4tan^{2}θ$ = $4sec^{2}θ$ so $\int{\frac{dx}{(4+9x^{2})^{2}}}$ = $\int{\frac{\frac{2}{3}sec^{2}θ}{16sec^{4}θ}dθ}$ = $\frac{1}{24}\int{cos^{2}θ}dθ$ = $\frac{1}{24}(\frac{1}{2}θ+\frac{1}{2}sinθcosθ+C$ = $\frac{1}{48}(θ+sinθ+cosθ)+C$ $x$ = $0$ then $θ$ = $0$ $x$ = $1$ then $tanθ$ = $\frac{3}{2}$ $sinθ$ = $\frac{3}{\sqrt {13}}$ $cosθ$ = $\frac{2}{\sqrt {13}}$ $\int_0^1{\frac{dx}{(4+9x^{2})^{2}}}$ = $\frac{1}{48}(θ+sinθ+cosθ)|_0^{tan^{-1}(\frac{3}{2})}$ = $\frac{1}{48}tan^{-1}(\frac{3}{2})+\frac{1}{104}$
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