The domain of a function is the set of values for which the function is defined; i.e. the function outputs a value for an input from the domain. That means that we must be able to plug in numbers for x and get numbers from y.
We can't take the square root of negative numbers (ignoring imaginary numbers), so that means we can take the square root of any non-negative number; i.e. we can take the square root of zero, and any positive number.
Therefore, any function that can take in values of x that are zero or more than zero has the same domain as the given function. So
is a function that has the same domain as 
.
We can't take the square root of negative numbers (ignoring imaginary numbers), so that means we can take the square root of any non-negative number; i.e. we can take the square root of zero, and any positive number.
Therefore, any function that can take in values of x that are zero or more than zero has the same domain as the given function. So