Express cos^4x and sin^4x cos^2x in terms of cosines of multiples of x How would you approach this question?
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Start with one of the well-known trig identities: cos(2x) = 2cos^2x - 1, so cos^2x = 1/2(1+cos(2x). Also use sin^4x = (sin^2x)^2 = (1 - cos^2x)^2.