Final answer:
Alternate exterior angles are congruent angles formed when two parallel lines are intersected by a transversal, located on opposite sides and outside of the parallel lines. They are used to find angle measures and prove line parallelism in geometry.
Step-by-step explanation:
Alternate exterior angles are formed when two parallel lines are intersected by a transversal. These angles are located on opposite sides of the transversal and are outside the parallel lines. By the Alternate Exterior Angles Theorem, they are congruent, which means they have equal measures. This theorem is a staple concept in geometry that helps in understanding the properties of parallel lines and transversals. When you're working with these angles, you are frequently using them to solve problems where you need to find unknown angle measures or prove lines are parallel.