Calculus: Early Transcendentals 8th Edition

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

Chapter 16 - Section 16.9 - The Divergence Theorem - 16.9 Exercise - Page 1145: 11

Answer

$\pi$

Work Step by Step

The Divergence Theorem states that $\iint_S \overrightarrow{F}\cdot d\overrightarrow{S}=\iiint_Ediv \overrightarrow{F}dV $ Here, $S$ is a closed surface and $E$ is the region inside that surface. $div F=\dfrac{\partial a}{\partial x}+\dfrac{\partial b}{\partial y}+\dfrac{\partial c}{\partial z}$ This implies that $div F=\dfrac{\partial (2x^3+y^3)}{\partial x}+\dfrac{\partial (y^3+z^3)}{\partial y}+\dfrac{\partial (3y^2z)}{\partial z}$ $div F=6x^2+3y^2+3y^2=6(x^2+y^2)$ Now, we have $\iiint_E 6(x^2+y^2) dV=\int_{0}^{2 \pi}\int_0^{1} \int_0^{1-r^2} 6r^2 r dz dr d\theta$ $=\int_{0}^{2 \pi}\int_0^{1} [6r^3 z]_0^{1-r^2} dr d\theta$ $=\int_{0}^{2 \pi}[\dfrac{3r^4}{2}-r^6]_{0}^{1} d\theta$ $=\int_{0}^{2 \pi}(\dfrac{3}{2}-1) d\theta$ $=[\dfrac{\theta}{2}]_0^{2 \pi}$ $=\pi$
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