dx/dy=(2y+x)/y=2+x/y
令x/y=u,x=yu,x'=u+yu'
u+yu'=2
yu'=2-u
du/(2-u)=dy/y
ln(2-u)=lny+C1=ln(e^C1*y)
2-u=Cy
2-x/y=Cy