看图片
lim(x->π/3) (1-2cosx)/sin(x-π/3)=lim(x->π/3) (1-2cosx)/(x-π/3)=lim(x->π/3) (1-2cosx)/(x-π/3) (0/0 分子分母分别求导)=lim(x->π/3) 2sinx=2sin(π/3)=√3
利用诺必达法则，分子分母同时求导再取极限，步骤见下图
