MathDB
Intersection point of perpendicular bisectors satisfies property

Source: Mexico National Olympiad Mock Exam 2019 P6

October 16, 2019
geometrysymmedianCircumcenterperpendicular bisector

Problem Statement

Let ABCABC be a scalene triangle with circumcenter OO, and let DD and EE be points inside angle BAC\measuredangle BAC such that AA lies on line DEDE, and ADB=CBA\angle ADB=\angle CBA and AEC=BCA\angle AEC=\angle BCA. Let MM be the midpoint of BCBC and KK be a point such that OKOK is perpendicular to AOAO and BAK=MAC\angle BAK=\angle MAC. Finally, let PP be the intersection of the perpendicular bisectors of BDBD and CECE. Show that KO=KPKO=KP.
Proposed by Victor Domínguez