The answer is below.
Work Step by Step
1. We know that if two lines are cut by a transversal, then the corresponding angles are congruent. 2. By definition, the alternate exterior angle of one angle forms a vertical angle with its corresponding angle. 3. According to the vertical angle theorem, vertical angles are congruent. 4. Thus, the second corresponding angle, which is equal to the first angle, in congruent to the alternate exterior angle of the first angle. 5. Therefore, alternate exterior angles are congruent.