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Source: Sharygin Correspondence Round P1

March 6, 2024
geometryincenterangle bisector

Problem Statement

Bisectors AIAI and CICI meet the circumcircle of triangle ABCABC at points A1,C1A_1, C_1 respectively. The circumcircle of triangle AIC1AIC_1 meets ABAB at point C0C_0; point A0A_0 is defined similarly. Prove that A0,A1,C0,C1A_0, A_1, C_0, C_1 are collinear.
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