1. The problem statement, all variables and given/known data I want to prove that coefficients of potential are non-negative. i.e. Pij ≥ 0 2. Relevant equations By coefficients of potential method we know that in a system of conductors the potential on ith conductor is related to charges on conductors by: [itex]\Phi[/itex]i = [itex]\sum[/itex] Pij Qj 3. The attempt at a solution It is written in Reitz and Milford that it is hard to prove in a rigorous way. I think that we should use Pii ≥ Pij.