MathDB
Perfect Hexagon in China MO

Source: CMO 2024 P5

November 29, 2023
geometrycircumcircle

Problem Statement

In acute ABC\triangle {ABC}, K{K} is on the extention of segment BCBC. P,QP, Q are two points such that KPAB,BK=BPKP \parallel AB, BK=BP and KQAC,CK=CQKQ\parallel AC, CK=CQ. The circumcircle of KPQ\triangle KPQ intersects AKAK again at T{T}. Prove that: (1) BTC+APB=CQA\angle BTC+\angle APB=\angle CQA. (2) APBTCQ=AQCTBPAP \cdot BT \cdot CQ=AQ \cdot CT \cdot BP.
Proposed by Yijie He and Yijuan Yao