If a diagonal line crosses two horizontal parallel lines transversally, it forms four pairs of corresponding angles, two pairs of alternate interior angles and two pairs of alternate exterior angles.
The line crosses the two lines in two meeting points, forming two sets of four angles around the points. If we name the angles around the upper point with numbers from one to four, going clockwise and starting from the one on the upper-right side of the transversal line, and the angles around the lower point of crossing with numbers from five to eight in the same order, it would mean that:
- The corresponding angle pairs are 4 and 8, 1 and 5, 2 and 6, and 3 and 7.
- Alternate interior angle pairs are 3 and 5, and 2 and 8
- Alternate exterior angles are 1 and 7, and 4 and 6
Draw it and you will see exactly how it goes, hope I helped.
