If $x + y + z = {180^o},$ then $\cos 2x + \cos 2y - \cos 2z$ is equal to
If $x + y + z = {180^o},$ then $\cos 2x + \cos 2y - \cos 2z$ is equal to
- A
$4\sin x.\,\sin y.\,\sin z$
- B
$1 - 4\sin x.\,\sin y.\,\cos z$
- C
$4 sin x. sin y. sin z -1$
- D
$\cos A.\cos B.\cos C$
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- [IIT 1977]