olymmath

IGO 2021 A3

  • Advanced

Consider a triangle ABCABC with altitudes AD,BEAD, BE , and CFCF , and orthocenter HH . Let the perpendicular line from HH to EFEF intersects EF,ABEF, AB and ACAC at P,TP, T and LL , respectively. Point KK lies on the side BCBC such that BD=KCBD=KC . Let ω\omega be a circle that passes through HH and PP , that is tangent to AHAH . Prove that circumcircle of triangle ATLATL and ω\omega are tangent, and KHKH passes through the tangency point.

Dataset text AI-MO AoPS. Quoted with source.

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