IMO 2022 Shortlist G7
Let ABC and A1 B1 C1 be two triangles having the same circumcircle ω, and the same orthocentre H. Let Ω be the circumcir...
Category: Geometry
Problem
Let ABC and A1 B1 C1 be two triangles having the same circumcircle ω, and the same orthocentre H. Let Ω be the circumcircle of the triangle determined by the lines AA1 , BB1 and CC1 . Prove that H, the centre of ω, and the centre of Ω are collinear. (Denmark)