A + (240^ + A) + (240^ - A) = - Vidyadip

MCQ

$\cos A + \cos (240^\circ + A) + \cos (240^\circ - A) = $

A
$\cos A$
✓
$0$
C
$\sqrt 3 \sin A$
D
$\sqrt 3 \cos A$

✓

Answer

Correct option: B.

$0$

b
(b) $\cos A + \cos \,({240^o} + A) + \cos \,({240^o} - A)$

$ = \cos A + 2\cos {240^o}\cos A$

$ = \cos A\{ 1 + 2\cos ({180^o} + {60^o})\} $

$= \cos A\,\left\{ {1 + 2\,\left( { - \frac{1}{2}} \right)} \right\}$

$ = 0$.

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