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KöMaL problem A, 2019

Geometry Difficulty 9.0 IMO level Prove it Hungary

In quadrilateral ABCDABCD, AB=BC=12DAAB=BC=\frac1{\sqrt2}DA, and ∠ABC\angle ABC is a right angle. The midpoint of side BCBC is EE, the orthogonal projection of CC on ADAD is FF, and the orthogonal projection of BB on CDCD is GG. The second intersection point of circle BCFBCF (with center HH) and line BGBG is KK, and the second intersection point of circle BHCBHC and line HKHK is LL. The intersection of lines BLBL and CFCF is MM. The center of the Feurbach circle of triangle BFMBFM is NN. Prove that ∠BNE\angle BNE is a right angle.

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