ISL 2019 G7
The incircle of acute-angled scalene triangle has centre and meets sides , , and at , and , respectively. The line through perpendicular to meets again at . Line meets again at . The circumcircles of triangles and meet again at . Prove that lines and meet on the external bisector of angle . (India) Common remarks. Throughout the solution, denotes the directed angle between lines and , measured modulo .
Dataset text NuminaMath olympiads. Quoted with source.
Official text: IMO 2019 Shortlist booklet, page 10.
Solutions
Official solution Solution 1 by the IMO Problem Selection Committee
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