trig identities
posted by Sean .
Find the exact value of cos (2theta) given csc theta = 8/3 and 0 < theta < pi/2

cscx = 8/3
sinx = 3/8
cosx = sqrt [1  sin^2x] = (sqrt55)/8
cos(2x) = 2 cos^2x 1 = 46/64 = 23/32
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