The method shown by the other tutor for finding the inverse of a function is one standard method.
For most relatively simple functions, you can also find the inverse informally by using the idea that an inverse function "un-does" what the function does.
To undo what the function does, the inverse function must perform the opposite operations in the opposite order.
The given function performs these operations on the input value:
(1) add 2;
(2) take the square root; and
(3) add 2
So the inverse function has to perform these operations:
(1) subtract 2;
(2) square the result; and
(3) subtract 2
