If AF = 4, ab = 7, find: (1) point out the rotation center and rotation angle; (2) find the length of de; (3) what is the position relationship between be and DF? And explain the reason

(1) According to the nature of rotation, we can know that: a △ AFD ≌ △ AEB, so AE = AF = 4, ∠ EAF = 90 ° and ∠ EBA = ∠ FDA, we can get the rotation center as point a, and the rotation angle is 90 ° or 270 °; (2) ∵ ab = 7, ≌ ad = AB = 7, ≌ de = ad-ae = 7-4 = 3; (3) be and DF are vertical

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