olymmath

ISL 2016 G5

    Let DD be the foot of perpendicular from AA to the Euler line (the line passing through the circumcentre and the orthocentre) of an acute scalene triangle ABCA B C. A circle ω\omega with centre SS passes through AA and DD, and it intersects sides ABA B and ACA C at XX and YY respectively. Let PP be the foot of altitude from AA to BCB C, and let MM be the midpoint of BCB C. Prove that the circumcentre of triangle XSYX S Y is equidistant from PP and MM.

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

    Official text: IMO 2016 Shortlist booklet, page 10.

    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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