particle 1 of charge q1 = +1.2 µC and particle 2 of charge q2 = -2.5 µC, are held at separation L = 14 cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the (a) x and (b) y coordinates of particle 3? I tried expressing the net electrostatic force on the third particle both on the x-axis and on the y-axis. The net force on both axis is =0. I introduced angles alpha and beta to express the angle between the x-axis and a line from particle 1 or particle 2 to particle 3, respectively. I can find the net electrostatic force using this and the Pythagorean theorem - but the expression has too many unknowns to be solved for x and y of the 3rd particle. What am I missing here? How should I go about solving this? Thanks.