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11 September, 20:11

Find the exact value of the trigonometric expression given cos (22.5).

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  1. 11 September, 22:08
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    Use the identity cos^2 (a/2) = 1/2 (1 + cos a) so

    cos^ 2 22.5 = cos^2 (45/2) = 1/2 (1 + cos 45) = 1/2 (1 + sqrt2 / 2) 4 = 1/2 + sqrt2/4

    cos 22.5 = sqrt (1/2 + sqrt2/4) Answer
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