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AP = CQ wanted, axis of MN related, midpoints of AD,BC where AB=CD

Source: 2022 Oral Moscow Geometry Olympiad grades 8-9 p3

April 17, 2022
equal segmentsgeometry

Problem Statement

In quadrilateral ABCDABCD, sides ABAB and CDCD are equal (but not parallel), points MM and NN are the midpoints of ADAD and BCBC. The perpendicular bisector of MNMN intersects sides ABAB and CDCD at points PP and QQ, respectively. Prove that AP=CQAP = CQ.
(M. Kungozhin)