Which of the following is a polynomial?
$$y^2+y^{-3}$$
On solving the equations,
$$y^2+\dfrac{1}{y^3}=0$$
$$y^2+y^{-3}=0$$
$$\because$$ After simplifying the equation, one of the term has a positive (-3) exponent.
So,following the ideal pattern of a polynomial$$y^2+\dfrac{1}{y^3}=0$$ is not a polynomial.