AF=√(AB^2+AF^2)=2√10,DE=DC/2=AB/2=3
∵∠AFB+∠ABF=90,∠AFB+∠DFE=90
∴∠ABF=∠DFE
∴RT△AFB≈RT△DEF
∴AF/FB=DE/EF,即
2/(2√10)=3/EF
EF=3√10