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US-TST 2020 Problem 2

    Two circles Γ1\Gamma_{1} and Γ2\Gamma_{2} have common external tangents ℓ1\ell_{1} and ℓ2\ell_{2} meeting at TT. Suppose ℓ1\ell_{1} touches Γ1\Gamma_{1} at AA and ℓ2\ell_{2} touches Γ2\Gamma_{2} at BB. A circle Ω\Omega through AA and BB intersects Γ1\Gamma_{1} again at CC and Γ2\Gamma_{2} again at DD, such that quadrilateral ABCDA B C D is convex. Suppose lines ACA C and BDB D meet at point XX, while lines ADA D and BCB C meet at point YY. Show that T,X,YT, X, Y are collinear.

    Dataset text NuminaMath olympiads. Quoted with source.

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