x=0时,y=0不存在dx/y^2
x<>0时,令t=y/x
xt^2(1-t)=1
x=1/(t^2(1-t))
dx=(3t-2)dt/(t^3(1-t)^2)
dx/y^2=dx/(x^2t^2)=(3t^2-2t)dt
积分得t^3-t^2=-1/x