1. you somehow changed the term of the function. I'll take the first version for further considerations.
If D is the domain of f and R is the range of f you got:
To calculate the inverse of f you change x and y and you have to change domain and range too:
. As you can see the inverse of f is not a function.
to c) Roughly speaking a continuously increasing (or decreasing) function has an inverse function too. Thus you have to divide f into two branches(?):
The decreasing branch:
and the increasing branch:
Solve the equation of the inverse of for y and you get the functions and their inverses as:
I've attached a drawing. Corresponding parts of the funcrtion and it's inverse are marked in similar colours.