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two intersecting circles, prove that a line bisects a segment

Source: 2012 Sharygin Geometry Olympiad Final Round 10.7

August 3, 2018
geometrycirclesbisection

Problem Statement

Consider a triangle ABCABC. The tangent line to its circumcircle at point CC meets line ABAB at point DD. The tangent lines to the circumcircle of triangle ACDACD at points AA and CC meet at point KK. Prove that line DKDK bisects segment BCBC.
(F.Ivlev)