IMO Shortlist 2014 problem G7


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7. svibnja 2017.
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Let ABC be a triangle with circumcircle \Omega and incentre I. Let the line passing through I and perpendicular to CI intersect the segment BC and the arc BC (not containing A) of \Omega at points U and V, respectively. Let the line passing through U and parallel to AI intersect AV at X, and let the line passing through V and parallel to AI intersect AB at Y. Let W and Z be the midpoints of AX and BC, respectively. Prove that if the points I, X, and Y are collinear, then the points I, W, and Z are also collinear.

(U.S.A.)

Izvor: https://www.imo-official.org/problems/IMO2014SL.pdf