dy/dx=(y-x)/(y+x)=(y/x-1)/(y/x+1),设y=xu，则dy/dx=u+xdu/dx,∫u/(u^2+1)du+∫1/(u^2+1)du=-∫1/xdx1/2(ln(u^2+1))+arctanu=-lnx+lnC1ln(C1√(x^2+y^2))=-arctany/x(x^2+y^2)=Ce^(-arctany/x)
请参考？
