A kite PQRS has congruent adjacent sides so that PQ=PR and SQ=SR. Its diagonals PR and QS intersect at O.
(a) Prove that △PQO≅△PRO.
(b) Prove that △SQO≅△SRO.
(c) Using the above, establish that ∠POQ=∠ROS and conclude that the diagonals of the kite are perpendicular. Present your reasoning in a logical chain of congruences.