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 548: 56



Work Step by Step

$cos~x+cos~4x=-2~sin(\frac{x+4x}{2})~sin(\frac{x-4x}{2})=-2~sin~\frac{5x}{2}~sin~(-\frac{3x}{2})=-2~sin~\frac{5x}{2}~(-sin~\frac{3x}{2})=2~sin~\frac{5x}{2}~sin~\frac{3x}{2}$ Remember that: $sin(-x)=-sin~x$
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