Algebra and Trigonometry 10th Edition

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

Chapter 7 - 7.4 - Sum and Difference Formulas - 7.4 Exercises - Page 538: 10


(a) $-\frac{\sqrt 2+\sqrt 6}{4}$ (b) $\frac{\sqrt 2-1}{2}$

Work Step by Step

(a) $cos(120°+45°)=cos~120°~cos~45°-sin~120°~sin~45°=-\frac{1}{2}\frac{\sqrt 2}{2}-\frac{\sqrt 3}{2}\frac{\sqrt 2}{2}=-\frac{\sqrt 2}{4}-\frac{\sqrt 6}{4}=-\frac{\sqrt 2+\sqrt 6}{4}$ (b) $cos~120°+cos~45°=-\frac{1}{2}+\frac{\sqrt 2}{2}=\frac{\sqrt 2-1}{2}$
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