University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 15 - Section 15.4 - Green's Theorem in the Plane - Exercises - Page 862: 27

Answer

$\dfrac{3 \pi}{8}$

Work Step by Step

We have $ dx=-3 \cos^2 t \sin t dt $ and $dy=3 \sin^2 t \cos t dt$ Consider, $A=\oint_{C} \dfrac{x}{2} dy - \dfrac{y}{2} dx$ After substituting the variables $ dx=-3 \cos^2 t \sin t dt $ and $dy=3 \sin^2 t \cos t dt$ , we have: $Area=\int_{0}^{2 \pi} \dfrac{1}{2} \times (\cos^3 t) \times (3 \sin^2 t \cos t dt) +\dfrac{sin^3 t}{2} ( -3 \cos^2 t \sin t dt) $ or, $=\dfrac{3}{2} \times \int_{0}^{2 \pi} \cos^2 t \times \sin^2 t (\cos^2 t+\sin^2 t) dt$ or, $=\dfrac{3}{16} \times \int_0^{2 \pi} [1-\cos 4t] dt$ or, $= [\dfrac{3t}{16}-\dfrac{3 \sin 4t}{64}]_0^{2 \pi}$ or, $ A=\dfrac{3 \pi}{8}$
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