Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 15 - Section 15.8 - Triple Integrals in Cylindrical Coordinates - 15.8 Exercise - Page 1050: 23

Answer

$\dfrac{1688 \pi}{15}$

Work Step by Step

Set up the integral. $I=\int_0^{\pi} \int_{0}^{2 \pi}\int_{2}^{3} (\rho^2 \sin^2 \phi) \times (\rho^2 \sin \phi) d\rho d\theta d\phi$ $=\int_0^{\pi} \int_{0}^{2 \pi} [\dfrac{\rho^5}{5}\sin^3 \phi]_2^3 d\theta d\phi$ $=( \dfrac{211}{5}) \int_0^{\pi} (2 \pi \sin^3 \phi ] d\phi$ $=\dfrac{422\pi}{5} \int_0^{\pi} \sin \phi \times (1-\cos^2 \phi) d\phi$ Substitute $\cos \phi=a; da=-\sin \phi d\phi$ $I= \dfrac{422\pi}{5} \int_1^{-1} (1-a^2)da=[\dfrac{422\pi}{5}][a-\dfrac{a^3}{3}]_1^{-1}$ $ =\dfrac{1688 \pi}{15}$
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