(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°