The figure shows an equilateral triangle ABC. A positive charge of +q is located at each of the three vertices A, B and C. Each of the side of the triangle is the length of a. A point charge Q(that may be positive or negative) is placed at the mid point between B And C. Determine an expression for the magnitude and sign of Q so that the net force on the charge at A is zero

The figure shows an equilateral triangle ABC. A positive charge of +q is located at each of the three vertices A, B and C. Each of the side of the triangle is the length of a. A point charge Q(that may be positive or negative) is placed at the mid point between B And C. Determine an expression for the magnitude and sign of Q so that the net force on the charge at A is zero