A) \[\cos A\]
B) 0
C) \[\sqrt{3}\sin A\]
D) \[\sqrt{3}\cos A\]
Correct Answer: B
Solution :
\[\cos A+\cos \,({{240}^{o}}+A)+\cos \,({{240}^{o}}-A)\] \[=\cos A+2\cos {{240}^{o}}\cos A\] \[=\cos A\{1+2\cos ({{180}^{o}}+{{60}^{o}})\}=\cos A\,\left\{ 1+2\,\left( -\frac{1}{2} \right) \right\}\] \[=0\].
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