SOLUTION: Find the exact value of cos(2theta) given csctheta=5/2 and 0<theta<pi/2

Question 943546: Find the exact value of cos(2theta) given csctheta=5/2 and 0
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
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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