The positive sign indicates that the point is to the left of the 2e charge as hypothesized; the negative sign indicates that the point is to the right of the 2e charge. When substituted into the equation defining potential, the negative root fails. Repeating this same procedure with the point x lying to the right of the 3e charge yields the points to the right of the 3e charge and to the left of the 3e charge. Again, the negative root fails in the equation defining potential, causing the point 1 to the left of the 3e charge to be eliminated. Thus the points to the left of the 2e charge, to the right of the 3e charge, and halfway between the charges are equipotential points. Starting from the halfway point and moving toward either charge causes the potential to increase. Once the charge has been passed, the potential again decreases, explaining why an equipotential point is possible on this side of the charge.
