Parallelogram ABCD & gt& gtAE is parallel to cf.

& gt& gt Angle EAO=FCO

And because of AC. Give BD to O > & gtAO=CO

Angel ·AOE = COF.

In a word, AOE of triangle equals COF.

2. Use the first question as an auxiliary line to connect AC, and get AOE AOE and COF congruences.

AE=CF=A 1E。

Because in triangles idh and gbh,

Angle d and angle b are equal, and the other diagonal line h is equal.

So the angle DHI=HGB=CGF=EIA 1.

Then the congruence of triangle A 1EI, CFG is proved by using the triangle angle edge theorem.

So E 1-FG