MathDB
Circles and the Euler line

Source: 2020 Iberoamerican #6

November 17, 2020
geometry

Problem Statement

Let ABCABC be an acute, scalene triangle. Let HH be the orthocenter and OO be the circumcenter of triangle ABCABC, and let PP be a point interior to the segment HO.HO. The circle with center PP and radius PAPA intersects the lines ABAB and ACAC again at RR and SS, respectively. Denote by QQ the symmetric point of PP with respect to the perpendicular bisector of BCBC. Prove that points PP, QQ, RR and SS lie on the same circle.