Answer
$\frac{1+\sqrt3}{2\sqrt2}$
Work Step by Step
Using the given identities and the known values: $\cos (15^\circ)=\pm\sqrt{\frac{1+\cos(30^\circ)}{2}}=\sqrt{\frac{1+\frac{\sqrt3}{2}}{2}}=\frac{1+\sqrt3}{2\sqrt2}$
Algebra 2 (1st Edition)
by Larson, Ron; Boswell, Laurie; Kanold, Timothy D.; Stiff, Lee
Published by
McDougal Littell
ISBN 10:
0618595414
ISBN 13:
978-0-61859-541-9
Chapter 14 Trigonometric Graphs, Identities, and Equations - 14.7 Apply Double-Angle and Half-Angle Formulas - Guided Practice for Examples 1, 2, and 3 - Page 956: 3
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