Given differential equation is .
$\left[1+\left(\frac{dy}{dx}\right)^{5}\right]^{2/ 3} = \frac{d^{3}y}{dx^{3}} $
Cubing both sides, we get
$\left[1+\left(\frac{dy}{dx}\right)^{5}\right]^{2} = \left( \frac{d^{3}y}{dx^{3}}\right)^3 $
$ \therefore $ Order = 3.