MCQ
$\cos A + \cos (240^\circ + A) + \cos (240^\circ - A) = $
- A$\cos A$
- ✓$0$
- C$\sqrt 3 \sin A$
- D$\sqrt 3 \cos A$
$ = \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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વિધાન 2 : $\left( {p \Rightarrow q} \right) \Leftrightarrow \left( { \sim q \Rightarrow \sim p} \right)$ એ નિત્ય સત્ય છે.