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: 13

Answer

$$\frac{9}{2} \pi$$

Work Step by Step

The area is bounded by $r=2 +\sin4 \theta$ 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}(2+\sin 4 \theta)^2 d \theta\\ &=\frac{1}{2} \int_0^{2 \pi}\left(4+4 \sin 4 \theta+\sin ^2 4 \theta\right) d \theta \\ & =\frac{1}{2} \int_0^{2 \pi}\left[4+4 \sin 4 \theta+\frac{1}{2}(1-\cos 8 \theta)\right] d \theta \\ & =\frac{1}{2} \int_0^{2 \pi}\left(\frac{9}{2}+4 \sin 4 \theta-\frac{1}{2} \cos 8 \theta\right) d \theta\\ &=\frac{1}{2}\left[\frac{9}{2} \theta-\cos 4 \theta-\frac{1}{16} \sin 8 \theta\right]_0^{2 \pi} \\ & =\frac{1}{2}[(9 \pi-1)-(-1)]\\ &=\frac{9}{2} \pi \end{aligned}
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