olymmath

TSTST 2018 Problem 3

    Let ABCA B C be an acute triangle with incenter II, circumcenter OO, and circumcircle Γ\Gamma. Let MM be the midpoint of AB‾\overline{A B}. Ray AIA I meets BC‾\overline{B C} at DD. Denote by ω\omega and γ\gamma the circumcircles of △BIC\triangle B I C and △BAD\triangle B A D, respectively. Line MOM O meets ω\omega at XX and YY, while line COC O meets ω\omega at CC and QQ. Assume that QQ lies inside △ABC\triangle A B C and ∠AQM=∠ACB\angle A Q M=\angle A C B. Consider the tangents to ω\omega at XX and YY and the tangents to γ\gamma at AA and DD. Given that ∠BAC≠60∘\angle B A C \neq 60^{\circ}, prove that these four lines are concurrent on Γ\Gamma.

    Dataset text NuminaMath olympiads. Quoted with source.

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