Answer
not a polynomial
Work Step by Step
Polynomials consist of one or more monomials and have the form:$$a_nx^n+a_{n-1}x^{n-1}+...+ a_1x+a+0$$
where $x$ is the variable, $a_n$ is the leading coefficient, and $n$ is a non-negative integer called the degree.
We can rewrite the expression as
$3x^2-\frac{5}{x}=3x^2-5x^{-1}$
We see that this is not a polynomial because we have $x$ with a negative exponent.