Cos A + cos (240° + A) + cos (240° - A) =

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3.Trigonometrical Ratios, Functions and Identities

easy

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

A

$\cos A$

B

$0$

C

$\sqrt 3 \sin A$

D

$\sqrt 3 \cos A$

Solution

(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$.

Standard 11

Mathematics

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