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Iranian geometry olympiad 2014

Source: Iranian geometry olympiad 2014

February 22, 2015
geometrygeometry proposed

Problem Statement

In the Quadrilateral ABCDABCD we have B=D=60 \measuredangle B=\measuredangle D = 60^\circ .MM is midpoint of side ADAD.The line through MM parallel to CDCD meets BCBC at PP.Point XX lying on CDCD such that BX=MXBX=MX.Prove that AB=BPAB=BP if and only if MXB=60\measuredangle MXB=60^\circ.
Author: Davoud Vakili, Iran