the domain is the set of all inputs for which a function is defined. when written as ordered pairs, the domain is the set of the first elements in the ordered pair.

For the domain is

since those are the first elements of the ordered pairs

we can input anything for x here. this is a polynomial, and so, the domain is given by:

For we have a restriction. we can only input the x-values that ensure that what is being square rooted is non-negative. thus we require

so what is the domain of the function here?