Algebra and Trigonometry 10th Edition

Published by Cengage Learning
ISBN 10: 9781337271172
ISBN 13: 978-1-33727-117-2

Chapter 7 - 7.5 - Multiple-Angle and Product-to-Sum Formulas - 7.5 Exercises - Page 549: 59


$cos\frac{3\pi}{4}-cos\frac{\pi}{4}=-\sqrt 2$

Work Step by Step

$cos\frac{3\pi}{4}-cos\frac{\pi}{4}=-2~sin(\frac{\frac{3\pi}{4}+\frac{\pi}{4}}{2})~sin(\frac{\frac{3\pi}{4}-\frac{\pi}{4}}{2})=-2~sin\frac{\pi}{2}~sin\frac{\pi}{4}=-2(1)(\frac{\sqrt 2}{2})=-\sqrt 2$
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