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ISL 2022 G5

    Let ABCA B C be a triangle, and let ℓ1\ell_{1} and ℓ2\ell_{2} be two parallel lines. For i=1,2i=1,2, let ℓi\ell_{i} meet the lines BC,CAB C, C A, and ABA B at Xi,YiX_{i}, Y_{i}, and ZiZ_{i}, respectively. Suppose that the line through XiX_{i} perpendicular to BCB C, the line through YiY_{i} perpendicular to CAC A, and finally the line through ZiZ_{i} perpendicular to ABA B, determine a non-degenerate triangle Δi\Delta_{i}. Show that the circumcircles of Δ1\Delta_{1} and Δ2\Delta_{2} are tangent to each other. (Vietnam)

    Dataset text NuminaMath olympiads. Quoted with source.

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