olymmath

ISL 2011 G5

    Let ABCA B C be a triangle with incenter II and circumcircle ω\omega. Let DD and EE be the second intersection points of ω\omega with the lines AIA I and BIB I, respectively. The chord DED E meets ACA C at a point FF, and BCB C at a point GG. Let PP be the intersection point of the line through FF parallel to ADA D and the line through GG parallel to BEB E. Suppose that the tangents to ω\omega at AA and at BB meet at a point KK. Prove that the three lines AE,BDA E, B D, and KPK P are either parallel or concurrent.

    Dataset text NuminaMath olympiads. Quoted with source.

    Official text: IMO 2011 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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