cos3t=3cost-4cos立方t可以具体化简步骤么。急用，谢谢cos3t
=cos(2t+t)
=cos2tcost-sin2tsint
=(2cos方t-1)cost -2sintcostsint
=2cos立方t -cost -2cost (1-cos方t)
=2cos立方t -cost -2cost+2cos立方t
=-3cost+4cos立方t
刚才写反了。大神，谢谢，