potential difference across a "square" 1. The problem statement, all variables and given/known data Two charges are placed at the corners of a square. One charge, +4.0 μ C, is fixed to one corner and another, −6.0 μ C, is fixed to the opposite corner. What charge would need to be placed at the intersection of the diagonals of the square in order to make the potential difference zero at each of the two unoccupied corners? 2. Relevant equations V= (k*q)/ r 3. The attempt at a solution I tried to make an equation adding V1+V2+V3=0, but I end up having two unknowns ("d" for distance and "q" for the unknown charge at the intersection). Can someone help me set up the equation please?