$\cos A + \cos (240^\circ + A) + \cos (240^\circ - A) = $
$\cos A + \cos (240^\circ + A) + \cos (240^\circ - A) = $
- A
$\cos A$
- B
$0$
- C
$\sqrt 3 \sin A$
- D
$\sqrt 3 \cos A$
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