Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 7 - Techniques of Integration - Review - Exercises - Page 579: 74

Answer

$4\ln \left(3\right)-4$

Work Step by Step

Given $$ y =\frac{1}{2+\sqrt{x}},\ \ \ y =\frac{1}{2-\sqrt{x}},\ \ \ x=1 $$ First, we find the intersection points \begin{aligned} \frac{1}{2+\sqrt{x}}&=\frac{1}{2-\sqrt{x}}\\ 2+\sqrt{x}&=2-\sqrt{x}\\ \sqrt{x}&=-\sqrt{x} \end{aligned} Then $x=0$ and $$ \frac{1}{2-\sqrt{x}}\geq \frac{1}{2+\sqrt{x}},\ \ \ 0\leq x\leq 1 $$ Hence \begin{aligned} A&= \int_{0}^{1} \left(\frac{1}{2-\sqrt{x}}-\frac{1}{2+\sqrt{x}}\right)dx\\ &= \int _0^1\frac{1}{2-\sqrt{x}}dx-\int _0^1\frac{1}{2+\sqrt{x}}dx \end{aligned} Let $u^2=x \ \to \ \ 2udu=dx$ and $x=0\ \to u=0 , x=1\ \ \to u=1 $ \begin{aligned} A&= \int_{0}^{1} \left(\frac{1}{2-\sqrt{x}}-\frac{1}{2+\sqrt{x}}\right)dx\\ &=2 \int _0^1\frac{u}{2-u}du-2 \int _0^1\frac{u}{2+u}du\\ &= 2\left(\int _0^1\frac{2}{2-u}du-\int _0^11du\right)-2\left(\int _0^1du-\int _0^1\frac{2}{2+u}du\right) \\ &= 2\left(2\ln \left(2\right)-1\right)-2\left(1-2\left(\ln \left(3\right)-\ln \left(2\right)\right)\right)\\ &=4\ln \left(3\right)-4 \end{aligned}
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