MathDB
concurrency wanted, intersecting circumcircles given

Source: 2010 Balkan Shortlist G7 BMO

April 4, 2020
geometrycircumcircleconcurrencyconcurrentprojective geometryradical axis

Problem Statement

A triangle ABCABC is given. Let MM be the midpoint of the side ACAC of the triangle and ZZ the image of point BB along the line BMBM. The circle with center MM and radius MBMB intersects the lines BABA and BCBC at the points EE and GG respectively. Let HH be the point of intersection of EGEG with the line ACAC, and KK the point of intersection of HZHZ with the line EBEB. The perpendicular from point KK to the line BHBH intersects the lines BZBZ and BHBH at the points LL and NN, respectively. If PP is the second point of intersection of the circumscribed circles of the triangles KZLKZL and BLNBLN, prove that, the lines BZ,KNBZ, KN and HPHP intersect at a common point.