IMO Shortlist 1994 problem G1

  Avg: 0,0
  Avg: 6,0
Dodao/la: arhiva
2. travnja 2012.
C and D are points on a semicircle. The tangent at C meets the extended diameter of the semicircle at B, and the tangent at D meets it at A, so that A and B are on opposite sides of the center. The lines AC and BD meet at E. F is the foot of the perpendicular from E to AB. Show that EF bisects angle CFD
Izvor: Međunarodna matematička olimpijada, shortlist 1994