[sin^3(wt)]'=3sin^2(wt)·cos(wt)·w=3w sin^2(wt)cos(wt)这是一个复合函数求导：f(g(u(x)))对x求导的结果是：f'(g)g'(u)u'(x)在这里,u(x)=wx,g(u)=sinu,f(g)=g^3
