Given: ABCDis a parallelogram ∠GEC ≅ ∠HFA and AE ≅FC.
Prove △GEC ≅ △HFA.

<GEC=<HFA
As
So
Cancel FE
Also
<CAH=<GCE(Alternative interior angles)
Henceforth
△GEC ≅ △HFA(ASA)