MathDB

9.6

Part of 2003 All-Russian Olympiad Regional Round

Problems(1)

<ABC=60^o if symmetrics of I wrt triangle sides and B are concyclic

Source: - All-Russian MO 2003 Regional (R4) 9.6

9/17/2024
Let II be the intersection point of the bisectors of triangle ABCABC. Let us denote by A′,B′,C′A', B', C' the points symmetrical to II wrt the sides triangle ABCABC. Prove that if a circle circumscribes around triangle A′B′C′A'B'C' passes through vertex BB, then ∠ABC=60o\angle ABC = 60^o.
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