BALKAN-SL 2018 G5
Let be an acute-angled triangle with and let be an arbitrary point on the extension of beyond . The circle intersects the rays , at points , respectively. The circumcircle of triangle intersects the lines again at points . The circumcircle of triangle intersects the lines again at points . Prove that the quadrilaterals and are cyclic and that their circumcenters coincide. (Greece)
Dataset text NuminaMath olympiads. Quoted with source.
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