Answer
All real numbers apart from $4$ and $9$.
Work Step by Step
We know that for rational expressions the domain is all the real numbers, excluding when the denominator is $0$.
$x^2-13x+36=x^2-4x-9x+36=x(x-4)-9(x-4)=(x-4)(x-9)$
Here the denominator is $0$, when $x=4$ or $x=9$, thus the domain is all real numbers apart from $4$ and $9$.
