1. The problem statement, all variables and given/known data Attached figure. 3 charges : q1, q2 and q3 are on a plane (for simplification). We want to compute the resulting charge at some point of the plane. 1/ Is it possible to sum (for computation) these charges to an arbitrary point A? 2/ or B? 2. Relevant equations these ones ? http://www.ux1.eiu.edu/~cfadd/1160/Ch17/Vector.html http://hyperphysics.phy-astr.gsu.edu/hbase/electric/mulpoi.html 3. The attempt at a solution I supposse I can't do it directly. I may use force or voltage or electric field?