A charge Q is placed at each of the opposite corners of a square. A charge q is placed at each of the other two corners. If the net electrical force on Q is zero, then Q/q equals

It is given that F→A+F→B+F→D=0 WhereF→A ,F→B and F→D  are the forces applied by charges placed at A, B and D on the charge placed at C.⇒F→B+F→D=−F→A |F→B+F→D|=2kqQa2&|F→A|=kQ22a2 ∴2kqQa2=−kQ22a2⇒Qq=−22