∴AD=AE,
In △BAD and △CAE,
AB=AC∠BAD=∠CAEAD=AE,
∴△BAD≌△CAE.
∴∠ABD=∠ACE,
∵DF⊥AC,AD=CD,
∴AF=CF,
∴∠GAD=∠ACE,
∴∠GAD=∠ABD.
∠∠GDA =∠ADB,
∴△GDA∽△ADB.
∴ADDB=DGAD,
∴AD2=DG? BD。
(2)∫ADDB = DGAD,AD=CD,
∴CDDB=DGCD.
∠∠CDG =∠BDC,
∴△DCG∽△DBC.
∴∠DBC=∠DCG.
AB = AC,
∴∠ABC=∠ACB.
∵∠ABD=∠ACE,
∴∠ECB=∠DBC=∠DCG,
∴∠ECB=∠DCG.