First, the function:
is a polynomial function, therefore, its domain is all real numbers.
next, we have the function:
In this case, the domain must be all values for x where the square root on the denominator is positive, that is:
then, we have that the domain of this function is all the real numbers greater than 2.
Now, for the function:
the only value that would make the function undefined is x=2 ( since we cannot have a 0 in the denominator), then, the domain of the function f(x) is all the real numbers except 2.
Finally, for the function:
We have that the square root is defined only on the positive real numbers, therefore, the domain o this function is all positive real numbers including 0