Answer
$(-\infty, -3) \cup (-3, 3) \cup +\infty)$
Work Step by Step
Factor the denominator to obtain:
$f(x) = \dfrac{x}{(x-3)(x+3)}$
To find the domain of the given function, exclude the values of $x$ that will make the function undefined.
Note that the function is undefined when the denominator is equal to $0$. Thus, the value of $x$ can be any real number except the ones that will make the denominator equal to zero.
To find the values of $x$ that will make the denominator zero, equate each factor of the denominator to zero; then, solve each equation.
$\begin{array}{ccc}
&x-3=0 &\text{ or } &x+3-0
\\&x=3 &\text{ or } &x=-3\end{array}$
Thus, the value of $x$ can be any real number except $3$ and $-3$.
In interval notation,
Domain: $\color{blue}{(-\infty, -3) \cup (-3, 3) \cup +\infty)}$
