How do you apply the double angle formula for ${cos}^{2} 4 x - {sin}^{2} 4 x$ $cos^2 4x - sin^2 4x$ ?

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Answer 1 · 2015-04-29T17:27:17

Use trig identity: $cos 2 a = {cos}^{2} a - {sin}^{2} a$ $cos 2a = cos^2 a - sin^2 a$

$y = {cos}^{2} (4 x) - {sin}^{2} (4 x) = cos (8 x)$ $y = cos^2 (4x) - sin^2 (4x) = cos (8x)$ .

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