Solution: As shown in the figure, if APEB is a parallelogram, then ∠ 1=∠5, and it is known that ∠ 1=∠2, ∠ 2 = ∠ 5.

∠BOE=∠POC, (the two angles are equal), so △POC∽△EOB.

Get the ratio of both sides, such as BO/PO=OE/OC.

So △POB∽△EOC (a diagonal line is equal, the two sides are proportional, etc. )

Prove ∠6=∠7

It is proved that CDPE is also a parallelogram.

Because APEB is a parallelogram, EP=AB, EP‖AB, and because ABCD is a parallelogram, AB=CD, AB‖CD.

So EP=CD, EP‖CD, so CDPE is also a parallelogram.

Germany: 200 BC, 200 BC.

∠4+∠PDC+∠PCD+∠2= 180 degrees? =? ∠2+∠7+∠PDC+∠PCD

So < 4 = < 7.

Because APEB is a parallelogram, AB‖PE, ∠3=∠6.

So ∠3=∠7=∠4.