SOLUTION: Find the exact value for cos2x given sinx= square root5/5 All help is greatly appreciated! Thanks!

Question 872899: Find the exact value for cos2x given sinx= square root5/5
All help is greatly appreciated! Thanks!
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Find the exact value for cos(2x) given sin(x) = sqrt(5)/5
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cos(2x) = sin^2-cos^2 = sin^2-(1-sin^2) = 2sin^2(x)-1
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Your Problem:
cos(2x) = 2(sqrt(5)/5)^2 -1 = 2(1/5) - 1 = -3/5
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Cheers,
Stan H.
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