Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 7 - Trigonometric Identities and Equations - 7.4 Double-Angle and Half-Angle Identities - 7.4 Exercises - Page 692: 1


$\Rightarrow 1\rightarrow C$

Work Step by Step

$2\cos ^{2}\alpha -1=\cos 2\alpha \Rightarrow 2\cos ^{2}15-1=\cos \left( 2\times 15\right) =\cos 30^{0}=\dfrac {\sqrt {3}}{2}$ $\Rightarrow 1\rightarrow C$
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