∵DG=EF;AD=AE;∠ADG=∠AEF;∴⊿ADG≌⊿AEF,
∴AG=AF∴∠AGF=∠AFG,∠DAG=∠EAF
又∠AGF+DAG+∠ABC,∠AFG=∠EAF+∠ACB,
∴∠ABC=∠ACB
∴AB=AC