## Precalculus (10th Edition)

The denominator of a rational function cannot be $0$, hence $x^2+4$ should not be equal to $0$. However, the value of $x^2+4$ will never be equal to zero since the value of $x^2$ is always non-negative for real numbers, making the value of $x^2+4$ always positive. Thus, the domain of the given function is the set of all real numbers.