Use Theorem s(x+y)= s(x)c(y)+c(x)s(y) to show cos(4x)= Then apply this formula to find the value of cos(/8)
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Now apply the angle-sum identity for sine as required. Then use: in the resulting formula. I would suggest letting to get a quadratic in . Take the appropriate root.
Last edited by MarkFL; Nov 13th 2012 at 10:00 PM.
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