Final answer:
Alternate interior angles and alternate exterior angles created by a transversal crossing parallel lines are supplementary, meaning their measures add up to 180 degrees.
Step-by-step explanation:
When a transversal crosses a pair of parallel lines, it creates several pairs of angles. Among these, alternate interior angles and alternate exterior angles are types of angle pairs that are supplementary. Supplementary angles are two angles whose measures add up to 180 degrees. In the case of alternate interior angles, they are on opposite sides of the transversal and inside the two parallel lines. For alternate exterior angles, they are on opposite sides of the transversal but outside the parallel lines. Both types of angles are equal when the lines are parallel, which means that each pair sums up to 180 degrees and hence are supplementary.
Alternate interior angles are a pair of angles that are on opposite sides of the transversal and on the inside of the parallel lines. They are formed when a transversal intersects two parallel lines. For example, if angle 1 is 40 degrees, angle 2 will be 140 degrees, and together they add up to 180 degrees.