IMO Shortlist 2011 problem G8


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23. lipnja 2013.
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Let ABC be an acute triangle with circumcircle \Gamma. Let \ell be a tangent line to \Gamma, and let \ell_a, \ell_b and \ell_c be the lines obtained by reflecting \ell in the lines BC, CA and AB, respectively. Show that the circumcircle of the triangle determined by the lines \ell_a, \ell_b and \ell_c is tangent to the circle \Gamma.

Proposed by Japan
Izvor: Međunarodna matematička olimpijada, shortlist 2011