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IL-GILLIS 2021 Problem 7

    Triangle ABCABC is given. The circle ω\omega with center II is tangent at points D,E,FD,E,F to segments BC,AC,ABBC,AC,AB respectively. When ABCABC is rotated 180180 degrees about point II , triangle A′B′C′A'B'C' results. Lines AD,B′C′AD, B'C' meet at UU , lines BE,A′C′BE, A'C' meet at VV , and lines CF,A′B′CF, A'B' meet at WW . Line BCBC meets A′C′,A′B′A'C', A'B' at points D1,D2D_1, D_2 respectively. Line ACAC meets A′B′,B′C′A'B', B'C' at E1,E2E_1, E_2 respectively. Line ABAB meets B′C′,A′C′B'C', A'C' at F1,F2F_1,F_2 respectively. Six (not necessarily convex) quadrilaterals were colored orange: AUIF2,C′FIF2,BVID1,A′DID2,CWIE1,B′EIE2AUIF_2 , C'FIF_2 , BVID_1 , A'DID_2 , CWIE_1 , B'EIE_2 Six other quadrilaterals were colored green: AUIE2,C′FIF1,BVIF2,A′DID1,CWID2,B′EIE1AUIE_2 , C'FIF_1 , BVIF_2 , A'DID_1 , CWID_2 , B'EIE_1 Prove that the sum of the green areas equals the sum of the orange areas.

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    Dataset text AI-MO AoPS. Quoted with source.

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