Question

An equilateral triangle wire frame of side l having 3 point charges

Answer 1

3 point charges of +q are placed on an equilateral triangle. They will repel each other and go away from each other, so the charge which we want to keep in the centre should be negatively charged. Now apply electrostatic forces, conditions for equilibrium in the two perpendicular directions and there you are.

Let us consider the charge of the one to be kept at centroid to be -Q. Let the length of the side of equilateral triangle is a. Consider an equilateral triangle ABC, with centroid at D.