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PrintSAUDI ARABIAN IMO Booklet 2023
Saudi Arabia 2023 geometry
Problem
Let be an acute triangle. The line through perpendicular to intersects at . Let be the midpoint of and the circle of center and radius . The line intersects at such that and are not on the same side of and the line intersects at such that and are not on the same side of . If two intersection points of the circumcircles of triangles and lie on the line , prove that .
Solution
Note that the condition of the problem is that is the radical axis of two circles () and () which implies that has the same power to these circles. This gives us However, because is the center of and this means that . From this, we conclude that is the perpendicular bisector of and leads to .
Techniques
Radical axis theoremCoaxal circlesDistance chasing