IMO Shortlist 1998 problem G7


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2. travnja 2012.
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Let ABC be a triangle such that \angle ACB=2\angle ABC. Let D be the point on the side BC such that CD=2BD. The segment AD is extended to E so that AD=DE. Prove that


\angle ECB+180^{\circ }=2\angle EBC.

commentEdited by Orl.
Izvor: Međunarodna matematička olimpijada, shortlist 1998