JBMO-SL 2016 G1
Let be an acute angled triangle, let be its circumcentre, and let be points on the sides , respectively. The circle of radius , centred at , crosses the segment at and the circumcircle (c) of the triangle again at . Similarly, the circle of radius , centred at , crosses the segment at and the circle (c) again at . Finally, the circle of radius , centred at , crosses the segment at and the circle (c) again at . Prove that the quadrilaterals , and are all cyclic, and their circumcircles share a common point.

Dataset text NuminaMath olympiads. Quoted with source.
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