The given D.E. is \(\left(\cfrac{d^2y}{dx^2}\right)^2 +cos\left(\cfrac{dy}{dx}\right)=0\)
This D.E. has highest order derivative \(\cfrac{d^2y}{dx^2}\)
∴ order = 2
Since this D.E. cannot be expressed as a polynomial in differential coefficients, the degree is not defined.