Trigonometry 7th Edition

Published by Cengage Learning
ISBN 10: 1111826854
ISBN 13: 978-1-11182-685-7

Chapter 5 - Section 5.2 - Sum and Difference Formulas - 5.2 Problem Set - Page 290: 79



Work Step by Step

$\cos{(165)} = \cos{(120+45)} = \cos{(120)}\cos{(45)} - \sin{(120)} \sin{(45)}$ $\cos{(165)} = \dfrac{-1}{2} \times \dfrac{\sqrt{2}}{2} - \dfrac{\sqrt{3}}{2} \times \dfrac{\sqrt{2}}{2}$ $\cos{(165)} = \dfrac{-\sqrt{6}-\sqrt{2}}{4}$
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