Let  be the two non-zero vectors. Then, prove thatÂ
 are perpendicular if and only ifÂ
(i) Assume that  are perpendicular
                          ...(i)
                           ...(2)
Again, Â
                                    ...(3)
Fom (2) and (3), we get.
    Â
(ii) Assume thatÂ
                           Â