Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 11 - Multiple Integrals - 15.2 Exercises - Page 1011: 21

Answer

$\displaystyle \frac{e^{-6}+5}{2}$

Work Step by Step

$\displaystyle \int\int_{R}ye^{-xy}dA=\int_{0}^{3}\int_{0}^{2}ye^{-xy}dxdy=\int_{0}^{3}[\int_{0}^{2}ye^{-xy}dx]dy$ $\left[\begin{array}{l} \text{... treat y as a constant in the inner integral} \\ \displaystyle\int_{0}^{2}ye^{-xy}dx=y\cdot(-\frac{1}{y}[e^{-xy}]_{x=0}^{x=2})\\ \\ =[-e^{-xy}]_{x=0}^{x=2}\\ \\ =-e^{-2y}+1 \end{array}\right]$ $=\displaystyle \int_{0}^{3}(-e^{-2y}+1)dy$ $=[\displaystyle \frac{1}{2}e^{-2y}+y]_{0}^{3}$ $=\displaystyle \frac{1}{2}e^{-6}+3-(\frac{1}{2}+0)$ $=\displaystyle \frac{e^{-6}+5}{2}$
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