Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 14 Trigonometric Graphs, Identities, and Equations - Chapter Review - Page 968: 26



Work Step by Step

Using the given formula and the known values: $\cos195^\circ=\cos60^\circ\cos135^\circ-\sin60^\circ\sin135^\circ=\frac{1}{2}(-\frac{1}{\sqrt2})-\frac{\sqrt3}{2}\frac{1}{\sqrt2}=-\frac{\sqrt3+1}{2\sqrt2}$
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