∵ Quadrilateral ABCD is a parallelogram
∴AB=CD,AB∥CD
∴∠BAO=∠DCO (two straight lines are parallel and the internal dislocation angles are equal)
∠AOB=∠COD (equal to vertex angle)
∴ Triangle ABO≌ Triangle COD
∴AO=CO,BO=DO.
(2).
Because ABCD
It is a parallelogram.
therefore
OB=OD
OE=OF
therefore
BFDE is a parallelogram (a quadrilateral with its diagonal bisected is a parallelogram.
)