Triangle PQR and triangle SQR are constructed on opposite sides of the same line segment QR such that
∠PQR=∠SRQ and ∠PRQ=∠SQR.
(a) Prove that △PQR≅△SQR.
(b) Write the pairs of equal sides that follow from the congruence.
(c) What kind of quadrilateral is PQRS? Give a reason for your answer.