The proof is as follows: ∵AB=AC, DE=DF,

∴DEAB=DFAC.

∠∠EDF =∠A，

∴△DEF∽△ABC.

∴∠DEF=∠B=∠C.

∠∠BED+∠DEF+∠FEC =∠C+∠CFE+∠FEC = 180，

∴∠BED=∠CFE.

∴△BDE∽△CEF.

Proof: (2)∫△BDE∽△CEF

∴BDCE=DEEF.

∫△DEF∽△ABC，

∴DEEF=ABBC.∴BDCE=ABBC.