ABCD is a parallelogram whose diagonals AC and BD intersect at O.
a. (i) Prove that △AOB≅△COD.
b. (ii) From the congruence proved in part (i), identify a new pair of equal sides that involves point O.
c. (iii) Using the equal side obtained in part (ii) together with a suitable angle, prove that △BOC≅△AOD.
d. (iv) Hence, state the common numerical relationship among the four segments AO,BO,CO and DO.