trigonometry

Question: If $x+y+z={{180}^{o}},$ then $\cos 2x+\cos 2y-\cos 2z$ is equal to

1) $4\sin x.\,\sin y.\,\sin z$

2) $1-4\sin x.\,\sin y.\,\cos z$

3) $3\cos \theta -4\sin \theta $

4) $\cos A.\cos B.\cos C$

Solution:

Explanation: No Explanation

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