$1 + \cos 2x + \cos 4x + \cos 6x = $
$1 + \cos 2x + \cos 4x + \cos 6x = $
- A
$2\cos x\cos 2x\cos 3x$
- B
$4\sin x\,\cos 2x\cos 3x$
- C
$4\cos x\cos 2x\cos 3x$
- D
None of these
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