1. The problem statement, all variables and given/known data [PLAIN]http://img532.imageshack.us/img532/3751/39842434.png [Broken] Find the potential in all space for this configuration. 2. Relevant equations ..basic electrostatics stuff, I guess. 3. The attempt at a solution I can easily cancel the whole z=0 plane by placing a charge of -q under it, of course, but I have no idea what I should do about the half-sphere. I naturally went for placing a charge in the center of the sphere to cancel the other two, and I attempted this by calculating the potential on the top of the sphere ([PLAIN]http://img15.imageshack.us/img15/6324/kqr.gif, [Broken] if pythagoras was right) and negating that with another charge, but this naturally messes the z=0 plane. Is it some other configuration of charges that's symmetrical for the z=0 plane? I guess it has to be, but I have no idea what such configuration would also negate the potential of the sphere.