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geo equals ForeBoding For Dennis

Source: USAJMO 2020/4

June 21, 2020
USAJMOgeometry2020 USAJMOgeometry solvedAngle Chasingeasyusojmo

Problem Statement

Let ABCDABCD be a convex quadrilateral inscribed in a circle and satisfying DA<AB=BC<CDDA < AB = BC < CD. Points EE and FF are chosen on sides CDCD and ABAB such that BE⊥ACBE \perp AC and EF∥BCEF \parallel BC. Prove that FB=FDFB = FD.
Milan Haiman
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