首先确认E点在AC上,F点在AB上证明：在ED的延长线取一点P,使PD=ED∵BD=DC,PD=ED,∠BDP=∠CDE（对顶角相等）∴⊿BDP≌⊿CDE,则BP=EC∵⊿FDP与⊿FDE是Rt⊿,PD=DE,FD=FD∴⊿FDP≌⊿FDE,则EF=EP,在⊿FBP中,BF+BP＞FP即BF+...