Answer
$\Rightarrow 1\rightarrow C$
Work Step by Step
$2\cos ^{2}\alpha -1=\cos 2\alpha \Rightarrow 2\cos ^{2}15-1=\cos \left( 2\times 15\right) =\cos 30^{0}=\dfrac {\sqrt {3}}{2}$
$\Rightarrow 1\rightarrow C$
Precalculus (6th Edition)
by Lial, Margaret L.; Hornsby, John; Schneider, David I.; Daniels, Callie
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
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