What is two thirds of cos
A:
cos(2π/3)
=cos(π-π/3)
=-cosπ/3
=-1/2
What is cos ^ 3
sin 3x = 3 sin x - 4 (sin x)^3
cos 3x = - 3 cos x + 4 (cos x)^3
So: (COS x) ^ 3 = (COS 3x + 3 cos x) / 4
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