As shown in Figure 2, connect OA,OD,OE,OF,OP, and OQ. To prove QR//AB, we need to prove that
RFER=QFAQ.
By Menelaus' theorem, we have
RFER=PAEP⋅CFAC.
It is also easy to see that △AOC∼△OFC, hence
CFAC=S△OFCS△AOC=OF2OA2.
Therefore, RFER=PAEP⋅OF2OA2.
Thus, we need to prove that QFAQ=PAEP⋅OF2OA2, which is equivalent to
QFAQ⋅PEAP=OF2OA2.
On the other hand, by the tangent length theorem, we have
∠AOQ=∠AOF−∠QOF=21∠EOF−21∠DOF=21∠EOD=∠POE.
Similarly, ∠AOP=∠QOF.
Thus, QFAQ⋅PEAP=S△QOFS△AOQ⋅S△AOES△AOP
=OFsin∠QOFAOsin∠AOQ⋅OEsin∠POEAOsin∠AOP=OF2OA2.
Therefore, the conclusion holds.