IMO Shortlist 2011 problem G7


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Let ABCDEF be a convex hexagon all of whose sides are tangent to a circle \omega with centre O. Suppose that the circumcircle of triangle ACE is concentric with \omega. Let J be the foot of the perpendicular from B to CD. Suppose that the perpendicular from B to DF intersects the line EO at a point K. Let L be the foot of the perpendicular from K to DE. Prove that DJ=DL.

Proposed by Japan
Izvor: Međunarodna matematička olimpijada, shortlist 2011