When a transversal is perpendicular to a pair of parallel lines, all eight
angles are congruent.
There are also exterior angles, same-side exterior angles, and alter-
nate exterior angles. They are positioned by the same common-sense
rules as the interior angles.
Two lines are parallel if any one of the following statements is true:
- A pair of alternate interior angles is congruent.
- A pair of alternate exterior angles is congruent.
- A pair of corresponding angles is congruent.
- A pair of same-side interior angles is supplementary.
1 2
4 3
5 6
8 7
∠ 1 ∠ 2 ∠ 3 ∠ 4
∠ 5 ∠ 6 ∠ 7 ∠ 8
m∠1 = m∠2 = m∠3 = m∠ 4
m∠5 = m∠6 = m∠ 7
m∠8 = 90
501 Geometry Questions