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In quadrilateral ABCD,
Take a point F on the side of GD to make GF = CE. △ AGF ≌ △ Dec (a corner on both sides is equal, two triangles are congruent) ∠ AFG = ∠ DCE = 30 ° and AF = CD ≔ DF = dg-gf = BC = CD = AF ≌
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