(i) In a parallelogram, opposite sides are equal in length. AD = BC
(ii) In a parallelogram, opposite angles are equal in measure. ∠DCB = ∠DAB
(iii) In a parallelogram, diagonals bisect each other. Hence, OC = OA
(iv) In a parallelogram, adjacent angles are supplementary to each other. Hence, m∠DAB + m∠CDA =180°