∵四边形ABCD是矩形,∴∠B=∠C=∠BAD=90°,AB=CD,∴∠BEF+∠BFE=90°.∵EF⊥ED,∴∠BEF+∠CED=90°.∴∠BFE=∠CED.∴∠BEF=∠EDC.在△EBF与△DCE中, ∠BFE=∠CED EF=ED ∠BEF=∠EDC ,∴△EBF≌△DCE(ASA).∴BE=CD,∴BE=AB=6,∴AE= AB2+BE2 =6 2 .故答案为6 2 .