Three particles are fixed on an x axis. Particle 1 of charge q1 is at x = -a and particle 2 of charge q2 is at x = +a. If their net electrostatic force on particle 3 of charge Q is to be zero, what must be the ratio q1/q2 when particle 3 is at (a) x = +0.400a and (b) x = +1.69a?