Answer
The domain is $\{x\in\mathbb{R}|x \neq 5,-5\}$.
Work Step by Step
We know that, division by $0$ is not defined.
Hence the domain would be all real numbers except those that make the denominator zero.
Find the values of $x$ that will make the denominator $0$:
$\begin{align} x^2-25&=0 \\ (x+5)(x-5) &=0 \\x &=-5,5\end{align}$
Thus the domain is all real numbers except $-5,5$, that is, the domain is $\{x\in\mathbb{R}|x \neq 5,-5\}$.
