Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 16 - Section 16.4 - Green''s Theorem - 16.4 Exercise - Page 1160: 16

Answer

$\frac{\pi}{2}$

Work Step by Step

First let's graph our function and see our orientation. We draw the graph of cosx from $(\frac{-\pi}{2},0) to (\frac{\pi}{2},0)$ then the line segment from $(\frac{\pi}{2},0) to (\frac{-\pi}{2},0)$ When we graph this, we realize that our orientation is going clockwise meaning our orientation is negative, so before we set up our integral, there will be a negative sign in front of the integral. Now for the values, x is trapped from $-\pi/2$ to $\pi/2$. y is trapped from $0$ to $\cos x$. That is if we were to do dydx $∫cPdx+Qdy=∫∫D(dQdx−dPdy)DA$ We were given $F(x,y)=\lt e^- (^{x})+y^2 , e^{-y}+x^2 >$ $dQ/dx = 2x $ $dP/dy= 2y$ Our integral will be $-\int _{\frac{-\pi}{2}}^{\frac{\pi}{2}}\int ^{\cos x}_{0} (2x-2y) dydx $ $-\int _{\frac{-\pi}{2}}^{\frac{\pi}{2}} |2xy-y^2|^{\cos x}_{0}dx $ $-\int _{\frac{-\pi}{2}}^{\frac{\pi}{2}} 2x\cos x-\cos^2xdx $ For $2x\cos x$, we do integration by part $\int udv=uv-\int vdu$ $u=2x ,dV=\cos x $ $du=2 , V=\sin x$ We will get $-[|2x\sin x| _{\frac{-\pi}{2}}^{\frac{\pi}{2}} -\int _{\frac{-\pi}{2}}^{\frac{\pi}{2}} 2\sin x dx -\int_{\frac{-\pi}{2}}^{\frac{\pi}{2}} \cos^2xdx]$ $-[\pi-(\pi)(-1)+|2\cos x|_{\frac{-\pi}{2}}^{\frac{\pi}{2}}-\int_{\frac{-\pi}{2}}^{\frac{\pi}{2}}1/2+\cos 2x/2]$ $-[-\frac{x}{2}+\frac{\sin 2x}{4}]_{\frac{-\pi}{2}}^{\frac{\pi}{2}}$= $-[-\frac{\pi}{4}-\frac{\pi}{4}]$= $-[\frac{-\pi}{2}]$= $\frac{\pi}{2}$
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