Which of the following expressions is a polynomial? State the reason. If an expression is a polynomial,state whether it is a polynomial in one variable or not: $3x^2 + 5x - 7 + \frac{8}{x}$

(N/A) The given expression is $3x^2 + 5x - 7 + \frac{8}{x}$.
This can be rewritten as $3x^2 + 5x - 7 + 8x^{-1}$.
$A$ polynomial is an algebraic expression in which the exponents of the variables are non-negative integers.
In this expression,the term $8x^{-1}$ has an exponent of $-1$,which is a negative integer.
Therefore,the expression is not a polynomial.