The answer is below.
Work Step by Step
Steps of the proof: 1. We are told that CE is parallel to DF. 2. Whenever a line goes through two parallel lines, the alternate and corresponding angles are congruent (equal in value). 3. Since DE bisects DEF, DC and EF are parallel. 4. Since DC and EF are parallel, angle 3 and angle 6 are alternate angles. 5. From (2), we know that alternate angles are congruent, so these angles are congruent.