#### Answer

$\Rightarrow 1\rightarrow C$

#### Work Step by Step

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

Published by
Pearson

ISBN 10:
013421742X

ISBN 13:
978-0-13421-742-0

$\Rightarrow 1\rightarrow C$

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