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取AD的中點F,連接EF,∵平行四邊形ABCD,BC=2AB,E為BC的中點,∴AD‖BC,AD=BC=2AB=2BE=2AF=2DF,∴AB=BE=AF=DF,∴AF=BE,AF‖BE,∴四邊形AFEB是平行四邊形,∴EF=AB=AF=DF,∴∠AED=90°.故答案為:90°.
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