The document describes the electric force between three charged particles: (1) The force on charge Q1 due to charge Q2 is calculated when they are separated by a fixed distance d and Q2 = 1 Coulomb. (2) A third charge Q3 is introduced and placed as shown in the figure. The total electric force on Q1 due to Q2 and Q3 is then calculated. (3) The calculations involve using Coulomb's law and applying vector addition to determine the overall electric force on Q1 from the other two charges.