∵∠ACB = 90°,AF⊥AE
∴∠CAE = ∠DCB
∵BD⊥CD,EF⊥CD
∴∠CEA = ∠CBD
∵AC = CB
∴△ACE≌△CBD
∴CE = DB
∵E是CB的中点
∴2CE=CB = AC = 12cm
∴BD = CE = 6cm
∵∠ACB = 90°,AF⊥AE
∴∠CAE = ∠DCB
∵BD⊥CD,EF⊥CD
∴∠CEA = ∠CBD
∵AC = CB
∴△ACE≌△CBD
∴CE = DB
∵E是CB的中点
∴2CE=CB = AC = 12cm
∴BD = CE = 6cm