lim[x→0] (1/x)(1/x - cosx/sinx)=lim[x→0] (1/x)(sinx-xcosx)/(xsinx)=lim[x→0] (sinx-xcosx)/(x²sinx)分母等价无穷小代换变成x³因此分子泰勒公式需展到x³sinx=x-(1/6)x³+o(x³)xcosx=x...