olymmath

APMO 2024 Problem 5

  • Paper

Line ℓ\ell intersects sides BCB C and ADA D of cyclic quadrilateral ABCDA B C D in its interior points RR and SS respectively, and intersects ray DCD C beyond point CC at QQ, and ray BAB A beyond point AA at PP. Circumcircles of the triangles QCRQ C R and QDSQ D S intersect at N≠QN \neq Q, while circumcircles of the triangles PASP A S and PBRP B R intersect at M≠PM \neq P. Let lines MPM P and NQN Q meet at point XX, lines ABA B and CDC D meet at point KK and lines BCB C and ADA D meet at point LL. Prove that point XX lies on line KLK L.

Dataset text NuminaMath olympiads. Quoted with source.

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