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 Test - Page 969: 20



Work Step by Step

Using the given identities and the known values: $\cos (-\pi/8)=\pm\sqrt{\frac{1+\cos(-\pi/4)}{2}}=\sqrt{\frac{1+(\frac{1}{\sqrt2})}{2}}=\frac{\sqrt{2+\sqrt2}}{2}$
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