In △PQR, ∠PQR=∠PRQ. The perpendicular bisector of QR meets the circumcircle of △PQR again at S (other than Q and R).
a. (i) Prove that QS=RS.
b. (ii) Show that points P,Q,R and S are concyclic.
c. (iii) Prove that PS is a diameter of the circumcircle of △PQR.