olymmath

ISL 2011 G7

  • Answer

Let ABCDEFA B C D E F be a convex hexagon all of whose sides are tangent to a circle ω\omega with center OO. Suppose that the circumcircle of triangle ACEA C E is concentric with ω\omega. Let JJ be the foot of the perpendicular from BB to CDC D. Suppose that the perpendicular from BB to DFD F intersects the line EOE O at a point KK. Let LL be the foot of the perpendicular from KK to DED E. Prove that DJ=DLD J=D L.

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

Official text: IMO 2011 Shortlist booklet, page 10.

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D L=D J

Solutions

Official solution Solution 1 by the IMO Problem Selection Committee

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