MathDB
Romania Junior TST 2021 Day 3 P2

Source:

June 7, 2021
geometryromaniaRomanian TST

Problem Statement

Let OO be the circumcenter of triangle ABCABC and let ADAD be the height from AA (DBCD\in BC). Let M,N,PM,N,P and QQ be the midpoints of AB,AC,BDAB,AC,BD and CDCD respectively. Let C1\mathcal{C}_1 and C2\mathcal{C}_2 be the circumcircles of triangles AMNAMN and POQPOQ. Prove that C1C2AD\mathcal{C}_1\cap \mathcal{C}_2\cap AD\neq \emptyset.