Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 10 - Section 10.2 - Areas and Lengths in Polar Coordinates - 10.4 Exercises - Page 673: 8

Answer

$A=\pi\,\ln\,2\pi-\pi+\frac{1}{2}$

Work Step by Step

Setting up the integral using the formula for the area of a region in polar coordinates, we get: $$\frac{1}{2}\int_{1}^{2\pi}(\sqrt{ln\,\theta})^2\,d\theta$$ We can rewrite this integral as: $$\frac{1}{2}\int_{1}^{2\pi}ln\,\theta\,d\theta$$ Solving the integral, we get: $$\frac{1}{2}(\theta\,\ln\,\theta-\theta)\bigg\rvert_{1}^{2\pi}=\frac{1}{2}\bigg((2\pi\,\ln\,2\pi-2\pi)-(-1)\bigg)=\pi\,\ln\,2\pi-\pi+\frac{1}{2}$$
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