(2006? As shown in Linfen), the rectangular paper abcd is folded up along ae, so that the point B falls on the point F on the dc side. If the perimeter of △afd is 9 and the perimeter of △ecf is 3, the perimeter of rectangular abcd is

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Test center: folding transformation (folding problem). Analysis: Folding is a symmetrical transformation, which belongs to axial symmetry. According to the nature of axial symmetry, the shape and size of the figure are unchanged before and after folding, and the position changes, and the corresponding edges and angles are equal. Solution: from the nature of folding, af=ab, EF = BE. Therefore, the sum of the perimeters of a rectangle is equal to △afd, and △cfe is equal to 9.