General function for E Field for point charge

[ZedCar]

Homework Statement

Write down a general function where E=f(r,D) for sphere (D=3), (where D is a dimensionality parameter, which describes how many orthogonal directions x,y,z the field drops off from its maximum).

Homework Equations

The Attempt at a Solution

E=f(r,3)

Am I correct in thinking I place the 3 where I have, and retain the r as an r.
Then insert some function where the f is located?

 

[ZedCar]

anyone have any ideas?