olymmath

ISL 2010 G4

    Let II be the incenter of a triangle ABCA B C and Γ\Gamma be its circumcircle. Let the line AIA I intersect Γ\Gamma at a point D≠AD \neq A. Let FF and EE be points on side BCB C and arc⁡BDC\operatorname{arc} B D C respectively such that ∠BAF=∠CAE<12∠BAC\angle B A F=\angle C A E<\frac{1}{2} \angle B A C. Finally, let GG be the midpoint of the segment IFI F. Prove that the lines DGD G and EIE I intersect on Γ\Gamma. (Hong Kong)

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

    Official text: IMO 2010 Shortlist booklet, page 53.

    Solutions

    Official solution Solution 1 by the IMO Problem Selection Committee

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