令y/x=u,则y=ux,dy/dx=u+xdu/dx所以u+xdu/dx=u+1/uxdu/dx=1/uudu=dx/x两边积分：u^2/2=ln|x|+Cu^2=ln(x^2)+Cy^2/x^2=ln(x^2)+Cy^2=x^2(ln(x^2)+C)c=2
