You can put this solution on YOUR website! You are probably aware that you can't take the square root of a negative number and get a real number solution. So the domain of even roots can be found by setting the inside of the root>=0.
x^2+4>=0
x^2+4-4>=0-4
x^2>=-4
sqrt(x^2)>=sqrt(-4)
Only you can't take the square root of a negative number, so there is no number that x can't be.
The domain is all real numbers.
(