2021 USAMO Problems/Problem 1
Rectangles and are erected outside an acute triangle Suppose thatProve that lines and are concurrent.
Solution
Let be the second point of intersection of the circles and Then is cyclic with diameters and Similarly, points and are collinear.
Similarly, triples of points and are collinear.
(After USAMO 2021 Solution Notes – Evan Chen)
vladimir.shelomovskii@gmail.com, vvsss
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