Calculus 8th Edition

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

Chapter 15 - Multiple Integrals - 15.8 Triple Integrals in Spherical Coordinates - 15.8 Exercises - Page 1090: 21

Answer

$\dfrac{312,500 \pi}{7}$

Work Step by Step

The conversion of rectangular coordinates to spherical coordinates is given as: $x=\rho \sin \phi \cos \theta; y=\rho \sin \phi \sin \theta;z=\rho \cos \phi$ Here, $\rho=\sqrt {x^2+y^2+z^2}$; $\phi =\cos^{-1} [\dfrac{z}{\rho}]; \theta=\cos^{-1}[\dfrac{x}{\rho \sin \phi}]$ Now, $(x^2+y^2+z^2)^2=\rho^4$ Consider $I=\int_0^{\pi} \int_{0}^{2 \pi}\int_{0}^{5} (\rho^4) (\rho^2) \sin \phi d\rho d\theta d\phi=\int_0^{\pi} \int_{0}^{2 \pi}\int_{0}^{5} \rho^6 \times \sin \phi d\rho d\theta d\phi$ $[\int_0^{\pi} \sin \phi d\phi] \times [\int_{0}^{2 \pi}d\theta] \times [\int_{0}^{5} \rho^6 d\rho] =[-\cos \phi]_0^{\pi} \times [\theta]_{0}^{2 \pi} \times [\dfrac{\rho^7}{7}]_0^5$ Hence, we have $I=(2 \pi) (1+1) [ \dfrac{78125}{7}]=\dfrac{312,500 \pi}{7}$
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