(11)
We observe that equation (9) is a polynomial equation in y″′,  y″ and y′, equation (10)
is a polynomial equation in y′ (not a polynomial in y though) Degree of such differential
equations can be defined But equation (11) is not a polynomial equation in y′ and
degree of such a differential equation can not be defined By the degree of a differential equation, when it is a polynomial equation in
derivatives, we mean the highest power (positive integral index) of the highest order
derivative involved in the given differential equation