0
cos(3t) = cos(2t + t) = cos(2t)*cos(t) - sin(2t)*sin(t)
= [cos2(t) - sin2(t)]*cos(t) - 2*cos(t)*sin(t)*sin(t)
= [cos2(t) - sin2(t)]*cos(t) - 2*cos(t)*sin2(t)
then, since sin2(t) = 1 - cos2(t)
= [2*cos2(t) - 1]*cos(t) - 2*cos(t)*[1 - cos2(t)]
= 2*cos3(t) - cos(t) - 2*cos(t) + 2*cos3(t)
= 4*cos3(t) - 3*cos(t)
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