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: 20

Answer

$16 \pi$

Work Step by Step

Here, $V=\int_{-2}^2 \int_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}} \int_{x^2+z^2}^{8-x^2-z^2} dy dz dx$ $= \int_{-2}^2 \int_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}} [y]_{x^2+z^2}^{8-x^2-z^2} dz dx $ $= \int_{-2}^2 \int_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}} (8-x^2-z^2-x^2-z^2) dz dx $ $=\int_{-2}^2 \int_{-\sqrt{4-x^2}}^{\sqrt{4-x^2}} [8-2(x^2+z^2)] dz dx $ $=\int_{0}^{2\pi} \int_0^2 (8-2r^2) r dr d\theta$ $=\int_0^2 (8r-2r^3) dr \cdot \int_{0}^{2\pi} d \theta$ $= (2 \pi) [4r^2-\dfrac{r^4}{2}]_0^2$ $= (2 \pi) [4(2)^2-\dfrac{(2)^4}{2}$ $= 16 \pi$
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