可能会用到三倍角公式：
sin3α = 3sinα-4sin³α = 4sinαsin(60°+α)sin(60°-α)
cos3α = 4cos³α-3cosα = 4cosαcos(60°+α)cos(60°-α)
tan3α = (3tanα-tan³α)/(1-3tan²α) = tanαtan(π/3+α)tan(π/3-α)
不过,这几个公式在高考中不常见,但还是应有所了解的.