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: 20

Answer

Green's Theorem has been verified.

Work Step by Step

We can parameterize the curve as $x= \cos \theta; y= 2 \sin \theta$ and $ 0 \leq \theta \lt 2 \pi $ Green's Theorem states that: $\oint_CP\,dx+Q\,dy=\iint_{D}(\dfrac{\partial Q}{\partial x}-\dfrac{\partial P}{\partial y})dA$ The line integral is: $\oint_CP\,dx+Q\,dy=\int_{C} (2x-x^3y^5) \ dx +(x^3 y^8) \ dy$ Substitute $x= \cos \theta; y= 2 \sin \theta$ Then, we have: $\int_{C} (2x-x^3y^5) \ dx +(x^3 y^8) \ dy =\int_{0}^{2 \pi} 2 \cos \theta \sin \theta (16 \cos^2 \theta \sin^4 \theta+256 \cos^3 \theta \sin^7 \theta-1) d \theta$ By using a calculator we have: $\int_{0}^{2 \pi} 2 \cos \theta \sin \theta (16 \cos^2 \theta \sin^4 \theta+256 \cos^3 \theta \sin^7 \theta-1) d \theta = 7 \pi ...(1)$ Now, the double integral is: $\iint_{D}(\dfrac{\partial Q}{\partial x}-\dfrac{\partial P}{\partial y})dA=\iint_{D}(\dfrac{\partial (x^3 y^8)}{\partial x}-\dfrac{\partial (2x-x^3y^5)}{\partial y})dA$ or, $=\int_{-1}^1 \int_{2 \sqrt {1-x^2}}^{\sqrt{1-x^2}} 3x^2 y^8+5x^3y^4 dy dx$ By using a calculator, we have: $\int_{-1}^1 \int_{2 \sqrt {1-x^2}}^{\sqrt{1-x^2}} 3x^2 y^8+5x^3y^4 dy dx=7 \pi ....(2)$ Hence, from equations (1) and (2), Green's Theorem has been verified.
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