SOLUTION: please help me solve this: sin^2 2pi/5 - cos^2 2pi/5
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Question 238105: please help me solve this: sin^2 2pi/5 - cos^2 2pi/5
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
I'm not sure what you mean by "solve this." There is no equals sign and no variable.
The only thing I can think to do with this is to calculate a numerical approximation. First recognize that:
\ =\ \cos^2(x)\ -\ \sin^2(x))
Therefore
\ -\ \cos^2(x)\ =\ -\cos(2x))
hence
\ -\ \cos^2\left(\frac{2\pi}{5}\right)\ =\ -\cos\left(\frac{4\pi}{5}\right)\ \approx\ 0.809)
But not sure where you want to go from here.
John
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