【解答】解:(1)∵RT△ABC中,AC=6,BC=8,∠C=90°,∴AB2=AC2+BC2=100,∴AB=10;(2)∵AD平分∠CAB,∴∠DAC=∠DAE,在△DAC和△DAE中,AC=AE∠DAC=∠DAEAD=AD,∴△DAC≌△DAE(SAS);(3)∵△DAC≌△DAE,∴∠AED=∠ACD=90°,AE=AC=6,∴BE=AB-AE=4,∵∠B=∠B,∴△BDE∽△BAC,∴DEBE=ACBC,即DE4=68,∴DE=3.