In quadrilateral PQRS the following measurements are known: ∠PQR=70∘, ∠PSR=70∘ and ∠QPR=38∘.
a. (i) Prove that the four points P,Q,R and S are concyclic.
b. (ii) Calculate ∠PRQ.
c. (iii) Determine ∠PSQ. State clearly every theorem or property you use in each step.