Answer
1. ABCD is a parallelogram. (Given)
2. By definition, DF and EB are parallel.
3. DE and FB are perpendicular to the same line, AB.
4. If two lines are perpendicular to the same line, then they are parallel to each other.
5. Thus, both sets of sides of DEBF are parallel, so DEBF is a parallelogram.
6. Opposite sides of parallelograms are congruent, so FB and DE are congruent.
