2021 IMO Problems/Problem 3
Let be an interior point of the acute triangle with so that . The point on the segment satisfies , the point on the segment satisfies , and the point on the line satisfies . Let and be the circumcentres of the triangles and respectively. Prove that the lines , , and are concurrent.
https://youtu.be/cI9p-Z4-Sc8 [Video contains solutions to all day 1 problems]