Question 943546
Find the exact value of cos(2t) 
given csc(t) = 5/2 and 0 < t < pi/2
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 csc = r/y, so r = 5 and y = 2
 Then x = sqrt[5^2-2^2] = sqrt(21)
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 Therefore cos = x/r = sqrt(21)/5 and sin = 2/5
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 Ans: cos(2t) = cos^2 - sin^2 = (21/25)-(4/25) = 17/25
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 Cheers,
 Stan H.
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