MathDB
Some geometry

Source: St Petersburg Olympiad 2014, Grade 9, P6

October 27, 2017
geometryincenter

Problem Statement

Points A,BA,B are on circle ω\omega. Points CC and DD are moved on the arc ABAB, such that CDCD has constant length. I1,I2I_1,I_2 - incenters of ABCABC and ABDABD. Prove that line I1I2I_1I_2 is tangent to some fixed circle.
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