Question #518a5

1 Answer

Mar 13, 2017

cos x

Explanation:

Reminder of trig identity:
$cos 2 a = {cos}^{2} a - {sin}^{2} a$ $cos 2a = cos^2 a - sin^2 a$
In this case:
${cos}^{2} (\frac{x}{2}) - {sin}^{2} (\frac{x}{2}) = cos x$ $cos^2 (x/2) - sin^2 (x/2) = cos x$

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Question #518a5

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