Where p = 2 aq is the electric dipole moment.
r = distance of the point from the centre of the dipole.
θ = the angle between vector p and r.
For any point on the dipole axis, θ = 0 or π => cos θ = ± 1, we get
For any point on the equatorial plane, θ = π/2, => cos θ = 0, we get V = 0