How do you verify the identity $cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x$ ?

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Answer 1 · 2015-04-29T17:34:30

Use the trig identity: $cos 2a = 1 - 2.sin^2 a$
$cos 4x = 1 - 2.sin^2 (2x)$
$cos 2x = 1 - 2sin^2 (x)$

$y = cos 4x + cos 2x = 2 - 2.sin^2 (2x) - 2.sin^2 (x)$ .

How do you verify the identity cos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 xcos 4x + cos 2x = 2 - 2 sin^2 2x - 2 sin^2 x?