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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