MathDB
Quadrilateral

Source: St Petersburg Olympiad 2009, Grade 10, P2

August 30, 2017
geometrycircumcircle

Problem Statement

ABCDABCD is convex quadrilateral with AB=CDAB=CD. ACAC and BDBD intersect in OO. X,Y,Z,TX,Y,Z,T are midpoints of BC,AD,AC,BDBC,AD,AC,BD. Prove, that circumcenter of OZTOZT lies on XYXY.
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