Solution: ABCD is an isosceles ladder, which is easy to know.

OB=OC，OA=OD

∫∠ADB = 60

∴△ADO and △OBC are equilateral triangles.

AE = EO，OF=BF

∴EF=AB/2,DE⊥AC,CF⊥BD

DG = GC

∴EG=DG=GC=DC/2=AB/2

FG==DG=GC=DC/2=AB/2

∴EF=EG=FG

Triangle EFG is an equilateral triangle.