Presently, on the off chance that we see, as charges are indistinguishable, so the net compel on any of the corner because of other two corner-chargers is kq^2/r^ making a point 60* with each other.
Subsequently the net Electric drive because of these two is (rt.3) * kq^2/r^ along the line joining focus and the corner in outward bearing.
At that point, the electrostatic constrain on centroid is (rt.3) * kq^2/r^2 + kQ^2/(2r/3)^2 = 0
On tackling, we get, Q = - {(4*(rt.3)q^2)/9}^1/2
