Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 15 - Multiple Integrals - 15.8 Exercises - Page 1055: 24

Answer

$(\dfrac{8\sqrt 2-7}{6}) \pi$

Work Step by Step

Conversion of rectangular to cylindrical coordinate system gives: $r^2=x^2+y^2 \\ \tan \theta=\dfrac{y}{x} \\z=z$ Here, $x=r \cos \theta; y=r \sin \theta, z=z$ Let $V=\int_0^{2\pi} \int_{0}^{1}\int_{r^2}^{\sqrt{2-r^2}} r dz dr d\theta$ or, $=\int_0^{2\pi} \int_{0}^{1}[rz]_{r^2}^{\sqrt{2-r^2}} r dz dr d\theta=\int_0^{2\pi} \int_{0}^{1}(r\sqrt{2-r^2}-r^3) dr d\theta$ Plug $k=2-r^2$ and $dk=-2rdr$ Thus, $V=-\int_0^{2\pi} [\int_{2}^{1} (1/2) k^{1/2} dk -\int_0^1 r^3 dr] d\theta=\int_0^{2\pi} [\int_{1}^{2} (1/2) k^{1/2} dk -\int_0^1 r^3 dr] d\theta$ or, $V=\int_0^{2\pi} [\dfrac{1}{3}(2 \sqrt 2 -1-\dfrac{1}{4}) d\theta=\int_0^{2\pi} (\dfrac{8\sqrt 2-7}{12}) d\theta$ Hence, $V=(\dfrac{8\sqrt 2-7}{12}) [\theta]_0^{2\pi}=(\dfrac{8\sqrt 2-7}{6}) \pi$
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