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Consider, an electric dipole of length 2a having charges +q and -q . A point P is at a distance r from the centre of the dipole such that OP is making an angle θ with dipole moment p . CONSTRUCTION :- Extend OP to BP such that BC is perpendicular to BP, Draw AD perpendicular to BP. PROOF :- Now, β = r + aCosθ      .........(1)          α = r + aCosθ      .........(2) Let, 'V1' and 'V2' be the potential due to +q and -q respectively. Net electric potential at 'P' is -               V = V1 + V2             V = kq/α + k(-q)/β             From equation (1) and (2)            Also,       p = q.2a Therefore,               [  V = kpCosθ/(r² - a²Cos²θ)   ] Note :- For axial line, θ = 0         ...