15^ = - Vidyadip

MCQ

$\cos 15^\circ = $

✓
$\sqrt {\frac{{1 + \cos 30^\circ }}{2}} $
B
$\sqrt {\frac{{1 - \cos 30^\circ }}{2}}$
C
$ \pm \sqrt {\frac{{1 + \cos 30^\circ }}{2}} $
D
$ \pm \sqrt {\frac{{1 - \cos 30^\circ }}{2}} $

✓

Answer

Correct option: A.

$\sqrt {\frac{{1 + \cos 30^\circ }}{2}} $

a
(a) $\cos {15^o} = \sqrt {\frac{{1 + \cos (2 \times {{15}^o})}}{2}} $

$= \sqrt {\frac{{1 + \cos {{30}^o}}}{2}} $ .$\left( {\,\,\,\,\because \cos {{15}^o} > 0} \right)$

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