The relation between the intensity of the electric field of an electric dipole at a distance r from its centre on its axis and the distance r is where ($r\gg 2l)$

Three charges of $+2q$, $-q$ and $-q$ are placed at the corners $A$, $B$ and $C$ of an equilateral triangle of side $a$, as shown in the adjoining figure. Then the dipole moment of this combination is