1. The problem statement, all variables and given/known data Place a third charge q between two charges Q1 = -2Q and Q2= 3Q so they stay in electrostatic equilibrium. Knowing that the distance between Q1 and Q2 is equal L 2. Relevant equations (KQ1Q)/(QQ1)2 = (KQ2Q)/(QQ2)2 3. The attempt at a solution Let's start by saying that i know how to solve that problem, or at least how to formally solve it, there is just something i can't understand... So, let's try to solve... To have equilibrium |F1|=|F2| We can say that the distance between Q1 and Q, Q1Q=x and the distance between Q2 and Q, Q2Q=(L-x) We put the equation (KQ1Q)/(x)2 = (KQ2Q)/(L-x)2 At the end we get x = sqrt(2)*L/(sqrt(3)-sqrt(2) ----> A positive x And till here i get it... But in case we put x = Q2Q and (L-x) = Q1Q , we get at the end a Negative x I can't actually understand the meaning of a negative/positive distance... My question is, what is the real meaning of the 2 x's, why is one positive and why is one negative? And how can i understand if the charge q that we have placed is at the left of the left charge or at the right of the right charge? We know for example here, that the charge q MUST be in either the right purple circle or the left circle (non between the Q1 and Q2.