1. The problem statement, all variables and given/known data Charge 8e-18 C is on the y axis a distance 2 m from the origin and charge 9e-18 C is on the x axis a distance d from the origin. The Coulomb constant is 8.98755e9 Nm^2/C^2. What is the value of d for which the x component of the force on 9e-18 C is the greatest? 2. Relevant equations Coulomb's law: F = kq1q2/r^2 3. The attempt at a solution I tried to use Coulomb's law to find the net force and then to find the force in the x direction but I became very stuck. F = 8.98755e9 Nm^2/C^2 * 8e-18 C * 9e-18 C / (4 + d^2) My problem is I have two unknowns and I can't find the value of d. Please help if you can.