The method of image for spherical boundary conditions relies on a fact that two point charges with opposite signs, $q1$ and $-q2$ with $q1 > q2 > 0$, form a sphere of zero electric potential $V = 0$. Show this argument in different spatial dimensions: the two point charges with a distance $r$ form a sphere of zero electric potential in $d > 3$ dimensions. Also, find the radius of the sphere.
I calculated the potential for $n$ dimensions for one charge, now I have two of them, by the power of the total potential is zero, I have to derive the method of images and the radius for this hypothetical sphere. I have no idea where to start. A few hints would be really nice.