Maths Olympiad Prep

Track / Stage 6 / 13 of 400 #1493 of 2444

Problem 1493

National Olympiad, first round
Geometry Difficulty 6.0 Prove it KöMaL problem A · Hungary · 2015

In the acute angled triangle ABCABC, the midpoints of the sides BCBC, CACA and ABAB are DD, EE and FF, respectively. The foot of the altitude of the triangle starting from CC is T1T_1. On some line, passing through point CC but not containing T1T_1, the feet of the perpendiculars starting from AA and BB are T2T_2 and T3T_3, respectively. Prove that the circle DEFDEF passes through the center of the circle T1T2T3T_1T_2T_3.
Proposed by: Bálint Bíró, Eger
(5 pont)

This one wants a proof. Work it on paper, then check yourself against the publisher's own solution, linked below. Be honest about it: the record is only any use to you if it is.

Next problem →

We don't reproduce this publisher's solutions. Their own solution is here — work the problem first.

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