The quantitative relationship of (1) is: AE = CF
The positional relationship is: AE parallel CF
Proof: Because the quadrilateral ABCD is a parallelogram.
So OA=OC= 1/2AC.
OB=OD
Because OB=BE+OE
OD=OF+DF
BE=DF
So OE=OF= 1/2EF.
AC and EF are equally divided.
So the quadrilateral AECF is a parallelogram.
So AE=CF
AE parallel CF
(2) Proof: Because the quadrilateral AECF is a parallelogram.
AC=EF
The quadrilateral AECF is a rectangle.