RRH gets to and then says that but there are two values of y whose square is x+ 4.
If the original function is " with domain ", THEN with domain .
If the original function is " with domain , THEN with domain
RRH is also wrong when he writes . For example, if x= 1, which is certainly not equal to .
Follow the pattern RRH used (which is correct). From (which has natural domain all real numbers except 2), the inverse function is given by , where I have swapped x and y. Now solve for y.and