olymmath

ISL 2009 G1

Let ABCA B C be a triangle with AB=ACA B=A C. The angle bisectors of AA and BB meet the sides BCB C and ACA C in DD and EE, respectively. Let KK be the incenter of triangle ADCA D C. Suppose that ∠BEK=45∘\angle B E K=45^{\circ}. Find all possible values of ∠BAC\angle B A C.

Official text Transcription from NuminaMath olympiads, checked word for word against the official paper. Quoted with source.

Official text: IMO 2009 Shortlist booklet, page 10.

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60^{\circ} \text{ or } 90^{\circ}

Solutions

Official solution Solution 1 by the IMO Problem Selection Committee

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