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DANUBE 2007 Problem 2

    Let ABCDABCD be an inscribed quadrilateral and let EE be the midpoint of the diagonal BDBD . Let Γ1,Γ2,Γ3,Γ4\Gamma_1,\Gamma_2,\Gamma_3,\Gamma_4 be the circumcircles of triangles AEBAEB , BECBEC , CEDCED and DEADEA respectively. Prove that if Γ4\Gamma_4 is tangent to the line CDCD , then Γ1,Γ2,Γ3\Gamma_1,\Gamma_2,\Gamma_3 are tangent to the lines BC,AB,ADBC,AB,AD respectively.

    Dataset text AI-MO AoPS. Quoted with source.

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