IMO 1992 LL CAN5

Let I, H, O be the incenter, centroid, and circumcenter of the

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IMO 1992 LL CAN5

Origin: CAN

Problem

Let I, H, O be the incenter, centroid, and circumcenter of the nonisosceles triangle ABC. Prove that AI\parallelHO if and only if ∡BAC = 120◦.