dx/dy=(2xy-y²)/(x²-2xy)dy/dx=(x²-2xy)/(2xy-y²) 分子分母同时除以x²dy/dx=(1-1y/x)/[2y/x-(y/x)²]设y/x=uu+xu'=(1-2u)/(2u-u²)xdu/dx=(u³-2u²-2u+1)/(2u-u²)分...