The degree of the differential equation $\left( \frac{d^2y}{dx^2} \right)^2 + \left( \frac{dy}{dx} \right)^2 = x \sin \left( \frac{dy}{dx} \right)$ is

not defined

The correct answer is Option (4) → not defined ##

The degree of above differential equation is not defined because when we expand $\sin \left( \frac{dy}{dx} \right)$ we get an infinite series in the increasing powers of $\frac{dy}{dx}$.

Therefore its degree is not defined.