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concyclic projections wanted, inside a cyclic quadrilateral

Source: 2008 Oral Moscow Geometry Olympiad grades 8-9 p4

October 13, 2020
geometryConcyclicprojectionscyclic quadrilateral

Problem Statement

A circle can be circumscribed around the quadrilateral ABCDABCD. Point PP is the foot of the perpendicular drawn from point AA on line BCBC, and respectively QQ from AA on DCDC, RR from DD on ABAB and TT from DD on BCBC . Prove that points P,Q,RP,Q,R and TT lie on the same circle.
(A. Myakishev)