y/x=u
(x^2+u^2*x^2)*dx-2*x*u*x*(x*du+u*dx)=0
x^2*(1+u^2-2*u^2)dx-2*x^3*u*du=0 | :x^2
(1-u^2)*dx-2*x*u*du=0 | :x*(1-u^2)
(dx/x)-(2*u*du)/(1-u^2)=0
int