trigonometry

Question: If $A+B+C=\frac{3\pi }{2},$ then $\cos 2A+\cos 2B+\cos 2C=$



1) $1-4\cos A\,\cos B\,\cos C$
2) $4\sin A\,\,\sin B\,\,\sin C$
3) $1+2\cos A\,\cos B\,\cos C$
4) $1-4\sin A\,\,\sin B\,\,\sin C$
Solution: Explanation: No Explanation
Maximum & minimum values of trigonometric functions Conditional trigonometric identities

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