Express cos(2x) in terms of acos^2(x) + b
cos(2x)=cos2(x) - sin2(x)use sin2(x) = 1 - cos2(x)so cos(2x)=cos2(x) - (1 - cos2(x))cos(2x)=2cos2(x) - 1so a = 2 and b = -1
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