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: 58



Work Step by Step

$cos~120°+cos~60°=2~cos(\frac{120°+60°}{2})~cos(\frac{120°-60°}{2})=2~cos~90°~cos~30°=2(0)(\frac{\sqrt 3}{2})=0$
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