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Given sintheta=4/5, theta lies in Quadrant II, find cos (theta/2)

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1 Answer

sin x = 4/5
cos x = -3/5, by 3-4-5 Pythagorean triple and Q. II
cos x/2 = sqrt[(1/2)(1+cos x)] = sqrt[(1/2)(1-3/5)] = sqrt(5)/5