题目可能有错!应该为：cot(x/y)*sec²x/y*(-x/y²)=-2x/y²csc2x/ycot(x/y)*sec²x/y*(-x/y²)=(-x/y²)*(cos(x/y)/sin(x/y))*(1/(cos(x/y))^2)=(-x/y²)/(sin(x/y)*cos(x/y))(-2x/y&su...