先用洛必达法则,上下同时求导
lim[x->0](x-sinx)/x^3
=lim[x->0](1-cosx)/3x^2
然后用等价无穷小代换
=lim[x->0]1/2*x^2/3x^2
=lim[x->0]1/6
=1/6