Because the diagonal of parallelogram ABCD intersects with O.

So OA = oc be Σ df

And because the straight line EF passes through AC to O.

So ∠AOE =∠ Buddha

And because BE∑DF

So ∠OEA=∠OFC

Because OA=OC ∠AOE=∠FOC ∠OEA=∠OFC(AAS)

So △OAE is equal to △OCF.

So OE=OF