Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 10 - Parametric Equations and Polar Coordinates - 10.4 Areas and Lengths in Polar Coordinates - 10.4 Exercises - Page 713: 14

Answer

$$11\pi $$

Work Step by Step

The area is bounded by $r=3- 2\cos4 \theta$ for $\theta=0$ to $\theta=2\pi$. \begin{aligned} A & =\int_0^{2 \pi} \frac{1}{2} r^2 d \theta\\ &=\int_0^{2 \pi} \frac{1}{2}(3- 2\cos4 \theta)^2 d \theta\\ &=\frac{1}{2} \int_0^{2 \pi}\left(9- 12\cos4 \theta+ 4\cos^24\theta\right) d \theta \\ & =\frac{1}{2} \int_0^{2 \pi}\left[9- 12\cos4 \theta+ 2(1+\cos 8 \theta)\right] d \theta \\ & =\frac{1}{2} \int_0^{2 \pi}\left(11 - 12\cos4 \theta+2\cos 8 \theta\right) d \theta\\ &=\frac{1}{2}\left[11\theta - 3\sin4 \theta+\frac{1}{4}\sin 8 \theta\right]_0^{2 \pi} \\ & = 11\pi \end{aligned}
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