1. The problem statement, all variables and given/known data Three point charges, q1, q2 and q3 all on x-axis (i.e y=0 and z=0) +q1 at x = 0 -q2 at dist from origin x = a +q3 at dist from origin x = -2a where q1, q2 and q3 are magnitudes of the charges. Assuming q1 = q2 derive magnitude of q3 in order for there to be zero net force on q1. 2. Relevant equations Coulombs law F12 = (q1 * q2) / (r12)2 rhat12 3. The attempt at a solution attempt 1 in order for there to be no force on q1 then, -q2(a) = q3(2a) so q3 = (-q2*a)/2a = -q2/a bit too simplistic? or attempt 2 F12 = 1/4*∏*ε0 * (q1*q2) / (r12)2 rhat12 . F12 = 1/4*∏*ε0 * (q1*q2) / (a2) ex F13 = 1/4*∏*ε0 * (q1*q3) / (r13)2 * rhat12 F13 = 1/4*∏*ε0 * (q1*q3) / (-2a2) -ex Resultant magnitude F1 = 0 = 1/4*∏*ε0 * ((q1*q2) / (a2) ex + (q1*q3) / (-2a2) -ex agh, run out of input time, will be back Am I on the right track?