Maths Olympiad Prep

Library / /143 of 151

, 2024

Geometry Difficulty 9.0 IMO level Find the answer Hungary

Let ABCABC be an obtuse triangle, and let HH denote its orthocenter. Let ωA\omega_A denote the circle with center AA and radius AHAH. Let ωB\omega_B and ωC\omega_C be defined in a similar way. For all points XX in the plane of triangle ABCABC let circle Ω(X)\Omega(X) be defined in the following way (if possible): take the polars of point XX with respect to circles ωA\omega_A, ωB\omega_B and ωC\omega_C, and let Ω(X)\Omega(X) be the circumcircle of the triangle defined by these three lines.
With a possible exception of finitely many points find the locus of points XX for which point XX lies on circle Ω(X)\Omega(X).

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: KöMaL, licensed Rights held by KöMaL and the MATFUND Foundation. Statement reproduced verbatim; metadata (topic, difficulty) added by this project. Solutions are the publisher's, linked not copied.