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2017 MMATHS Tiebreaker p4 - < B_0A_0C_0 = 90^o iff <BAC = 120^o

Source:

October 8, 2023
geometryMMATHS

Problem Statement

In a triangle ABCABC, let A0A_0 be the point where the interior angle bisector of angle AA meets with side BCBC. Similarly define B0B_0 and C0C_0. Prove that ∠B0A0C0=90o\angle B_0A_0C_0 = 90^o if and only if ∠BAC=120o\angle BAC = 120^o.
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