Answer
All real numbers
Work Step by Step
The domain of the function is all real numbers, except for when the denominator is 0. Thus, we let the denominator equal 0:
$$x^2+4 = 0 \\ x= \sqrt{-4}$$
Because the square root of a negative number is not a real value, we see that the denominator will never equal 0. Thus, the domain is the set of all real numbers.
