如题所述
由平行四边形ABCD,得AB=CD,AD=BC.角DAB=60=角BCD.由E,F是AB,CD的中点,得BE=DF=AE=CF.由于角DAB=60,AB=2AD,得角BDA=90,AE=BE=AD=DE=DF=BF,得证
AD//BG,AG//BD,角BDA=90,得AGBD为矩形