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 - 15.7 Exercises - Page 1049: 22

Answer

$20 \pi$

Work Step by Step

Here, we have $V=\int_{-2}^2 \int_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}} (5-z) dz dx $ $=\int_{-2}^2 [5z-z^2]_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}}dx $ $=\int_{-2}^2 [5[\sqrt{4-x^2})+\sqrt{4-x^2}]-[\sqrt{4-x^2})+\sqrt{4-x^2}]^2]_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}}dx $ $=\int_{-2}^{2}(5) \sqrt{4-x^2} dx$ Suppose $x=2 \sin \theta$ and $ dx=2 \cos \theta d \theta$ $=\int_{-2}^{2} \sqrt{4-(2 \sin \theta)^2} (2 \cos \theta d \theta)$ $=10 \int_{-\pi/2}^{\pi/2}(2 \cos \theta)^2 d \theta$ $= 20 \int_{-\pi/2}^{\pi/2} (2\cos \theta+1)$ $=20 \pi$
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