证明:如答图所示,
过D作DH ∥ AC交BC于H,则∠ACB=∠DHB,DH ∥ CE,
∵AB=AC,
∴∠B=∠ACB.
∴∠B=∠DHB.
∴DB=DH.
∵BD=CE,
∴DH=CE.
∵DH ∥ CE,
∴△HDF ∽ △CEF.
∴
FD
FE =
DH
EC =1 .
即FD=FE.
证明:如答图所示,
过D作DH ∥ AC交BC于H,则∠ACB=∠DHB,DH ∥ CE,
∵AB=AC,
∴∠B=∠ACB.
∴∠B=∠DHB.
∴DB=DH.
∵BD=CE,
∴DH=CE.
∵DH ∥ CE,
∴△HDF ∽ △CEF.
∴
FD
FE =
DH
EC =1 .
即FD=FE.