Freddy makes the claim that the inverse function of the function ƒ(x), where f(x)=2x2+2, is f−1(x)=x−22−−−√ His work is shown below.

For ƒ(x) let y=2x2+2 then the inverse function is
x=2y2+22y2=x−2y2=x−22
y=x−22−−−√ therefore the inverse function of ƒ(x) is f−1(x)=x−22−−−√

In order for Freddie's claim to hold true, which of the following assumptions must be made?

A
The domain of ƒ(x) is x≥0.

B
The domain of ƒ(x) is x≥−2.

C
The domain of f−1(x) is x≥0.

D
The domain of f−1(x) is x≥−2.