First Note: f(g(x)) or g(f(x)) cannot be a value, since x isn't defined.
Consider that: x^1/2 = sqrt(x) and that the restriction of the domain for any radical function is that whatever is under the square root must be greater than or equal to 0.
EDIT:// if a single radical term is in the denominator, then it is strictly greater than 0. If there instead additional terms in the denominator, the entire denominator cannot equal 0.
If you wanted to set f(g(x)) = 0, then you will get the zeroes of the function, and since you know for square roots, the function tends to the right of the real line, then you can use it. use order of operations to solve. I prefer using the above method instead for more complex situations.