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.