MathDB
circumcircle, excircle, equal segments, parallel wanted

Source: 2018 Oral Moscow Geometry Olympiad grades 8-9 p3

July 25, 2019
geometrycircumcircleexcircleparallel

Problem Statement

On the extensions of sides CACA and ABAB of triangle ABCABC beyond points AA and BB, respectively, the segments AE=BCAE = BC and BF=ACBF = AC are drawn. A circle is tangent to segment BFBF at point NN, side BCBC and the extension of side ACAC beyond point CC. Point MM is the midpoint of segment EFEF. Prove that the line MNMN is parallel to the bisector of angle AA.