Thinking method: To prove that the area is equal is to prove congruence, or to prove that the base is equal, or to prove that the area difference is equal. This topic obviously does not meet the requirements of contract surplus or equal bottom, so we should start with the area difference.

Through the known conditions:

△BCE and△△ AED have the same height, and the bottom sum =CD.

S△BCE+S△AED=0.5*S parallelogram ABCD

In the same way; In a similar way

S△ADF=S△AED+S△DEF=0.5*S parallelogram ABCD

Summary: The area of triangle BEC and triangle DEF is equal.