Calculus: Early Transcendentals 8th Edition

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

Chapter 10 - Section 10.4 - Areas and Lengths in Polar Coordinates - 10.4 Exercises - Page 672: 3

Answer

$A=\frac{\pi}{2}$

Work Step by Step

Setting up the integral using the formula for the area of a region in polar coordinates, we get: $$\frac{1}{2}\int_{0}^{\pi} (sin\,x+cos\,x)^2 dx$$ Expanding the integrand, we can rewrite the expression as: $$\frac{1}{2}\int_0^\pi(sin^2x+2sinx\,cosx+cos^2x)dx$$ We can rearrange the terms slightly and get: $$\frac{1}{2}\int_0^\pi(sin^2x+cos^2x+2sinx\,cosx)dx$$ Using the Pythagorean trignometric identity and the double-angle identity for sine, we can rewrite the expression as: $$\frac{1}{2}\int_0^\pi(1+sin\,2x)dx$$. Evaluating the integral, we get: $$\frac{1}{2}(x-\frac{1}{2}cos\,2x)\bigg\rvert_{0}^{\pi}=\frac{\pi}{2}$$
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