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Circumcenter lies on circumcircle.

Source: Argentina Cono Sur TST 2024 P3

August 9, 2024
geometrycircumcircle

Problem Statement

Let ABCABC be an acute triangle. The point BB' of the line CACA is such that AA, CC, BB' are in that order on the line and BC=ABB'C=AB; the point CC' of the line ABAB is such that AA, BB, CC' are in that order on the line and CB=ACC'B=AC. Show that the circumcenter of triangle ABCAB'C' belongs to the circumcircle of triangle ABCABC.