(10)
sin
dy
dy
dx
⎛dx
⎞
+
⎜
⎟
⎝
⎠  = 0 (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