Given function V(r) = 2gm r is the function V or r.
Where, g is the universal gravitational constant.
In order to find it's inverse we need to solve it for r first.
We have 2gm is being multiplied with r on right side.
Reverse operation of multiplication is division. So we need to divide both sides by 2gm.

2gm crossed out on right side, we get

Switching V(r) and r, we get

Therefore, required inverse function is
.