Three point charges lie along the x axis. The positive charge q1 = 15.0uC and is at x = 2.00m (2.00 away from the origin), the positive q2 = 6.00uC is at the origin. The net force on q3 which is between q2 and q1 is 0. What is the x coordinate of q3?
My book (serway and jewett, 8ed, pg 665) says x = 0.775 from 3x^2 + 8x - 8 = 0
the other x = -3.44m
The book says the negative one is (and here I quote) "the magnitude of the forces on q3 are equal, but both forces are in the same direction".
Unfortunately I have no idea what that means, based on my knowledge, isn't the negative one just another point where it satisfies the conditon? So if it was moved to satisfy x = -3.44, then x = 0.755 would be rejected?