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quadrilateral with $AD=BC$

Source: 3-rd Taiwanese Mathematical Olympiad 1994

January 14, 2007
geometrycyclic quadrilateralgeometry unsolved

Problem Statement

Let ABCDABCD be a quadrilateral with AD=BCAD=BC and A^+B^=1200\widehat{A}+\widehat{B}=120^{0}. Let us draw equilateral ACP,DCQ,DBRACP,DCQ,DBR away from ABAB . Prove that the points P,Q,RP,Q,R are collinear.
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