MathDB
Proving ABCD inscribed(only with strange conditions)

Source: 1999 KJMO

June 30, 2024
geometryconvex quadrilateralinscribed quadrilateralKJMO

Problem Statement

There exists point OO inside a convex quadrilateral ABCDABCD satisfying OA=OBOA=OB and OC=ODOC=OD, and AOB=COD=90\angle AOB = \angle COD=90^{\circ}. Consider two squares, (1)square having ACAC as one side and located in the opposite side of BB and (2)square having BDBD as one side and located in the opposite side of EE. If the common part of these two squares is also a square, prove that ABCDABCD is an inscribed quadrilateral.