ρ = dx2d2y[1+(dxdy)2]3/2 ⇒ ρ (dx2d2y) = [1+(dxdy)2]3/2 On squaring both sides, we get ρ2(dx2d2y)2 = [1+(dxdy)2]3 Clearly, it is a second order differential equation of degree 2. Note that the higher order derivative is in the transcendental, then we do not determined the degree of that equation