SOLUTION: Determine cos2x if sin^(4)x = 25/36 when 0 < x < &#960;/2

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Question 1031206: Determine cos2x if sin^(4)x = 25/36 when 0 < x < π/2
Answer by ikleyn(52835) About Me  (Show Source):
You can put this solution on YOUR website!
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Determine cos2x if sin^(4)x = 25/36 when 0 < x < π/2
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If  sin%5E4%28x%29 = 25%2F36,  then  sin%5E2%28x%29 = 5%2F6  and 

cos%282x%29 = cos%5E2%28x%29+-+sin%5E2%28x%29 = %281-sin%5E2%28x%29%29+-+sin%5E2%28x%29 = 1+-+2%2Asin%5E2%28x%29 = 1+-+2%2A%285%2F6%29 = 1+-+5%2F3 = -2%2F3.


The info 0 < x < pi%2F2  is irrelevant.
It is not used in the solution, and the solution/the answer does not depend on this condition.