Determine whether the expression \(5x^{2} + 3x^{-1} + 7\) is a polynomial.

Step 1 ：Step 1: Recall that a polynomial is an expression of the form \(a_{n}x^{n} + a_{n-1}x^{n-1} + \dots + a_{2}x^{2} + a_{1}x + a_{0}\), where \(a_{n}, a_{n-1}, \dots, a_{2}, a_{1}, a_{0}\) are constants and the exponents are non-negative integers.

Step 2 ：Step 2: Look at the given expression \(5x^{2} + 3x^{-1} + 7\) and notice that the second term \(3x^{-1}\) has a negative exponent. This is not allowed in a polynomial.

Step 3 ：Step 3: Therefore, the given expression is not a polynomial.