olymmath

ISL 2023 G5

    Let ABCA B C be an acute-angled triangle with circumcircle ω\omega and circumcentre OO. Points D≠BD \neq B and E≠CE \neq C lie on ω\omega such that BD⊥ACB D \perp A C and CE⊥ABC E \perp A B. Let COC O meet ABA B at XX, and BOB O meet ACA C at YY. Prove that the circumcircles of triangles BXDB X D and CYEC Y E have an intersection on line AOA O. (Malaysia)

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

    Official text: IMO 2023 Shortlist booklet, page 9.

    Solutions

    Official solution Solution 1 by the IMO Problem Selection Committee

    The terms of the source let olymmath link to this solution but not copy it. Read the solution (IMO official site).

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