Answer:
Parallelogram = 2 pairs of parallel sides and opposite angles are equal
Triangle BEA and triangle DFC are equivalent by side angle side
Therefore, angle DCF is equivalent to angle BAE
Angles FEB and DFE are right angles due to them being supplementary angles with angles BEA and DFC, respectively.
This means triangles BEC and DFA are equivalent.
This means angles FCB and EAD are equivalent, which means angles BCD and DAB are equivalent.
This also means angles ABC and ADC are equivalent.
Opposite angles equivalent = parallelogram
