Consider the equation (y+x2+y2)dx−xdy=0(y + \sqrt{x^2+y^2})dx - x dy = 0(y+x2+y2)dx−xdy=0. What substitution is most appropriate?
y=vxy = vxy=vx
y=v+xy = v+xy=v+x
x=vyx = vyx=vy
v=x2+y2v = x^2+y^2v=x2+y2