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A good Parallelogram

Source:

February 3, 2015
geometryparallelogramcircumcirclepower of a pointradical axisgeometry proposed

Problem Statement

Suppose that ABCDABCD is a parallelogram such that DAB>90DAB>90. Let the point HH to be on ADAD such that BHBH is perpendicular to ADAD. Let the point MM to be the midpoint of ABAB. Let the point KK to be the intersecting point of the line DMDM with the circumcircle of ADBADB. Prove that HKCDHKCD is concyclic.
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