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ST bisects BC, <ASO = <ACO, <ATO =< ABO

Source: Switzerland - Swiss MO 2013 p7

July 16, 2020
geometrybisects segmentequal angles

Problem Statement

Let OO be the center of the circle of the triangle ABCABC with ABACAB \ne AC. Furthermore, let SS and TT be points on the rays ABAB and ACAC, such that ASO=ACO\angle ASO = \angle ACO and ATO=ABO\angle ATO = \angle ABO. Show that STST bisects the segment BCBC.