1. 3-2 Properties of Parallel Lines

2. Postulates Postulate 10 Postulate 11
If two parallel lines are cut by a transversal, then corresponding angles are congruent.
Postulate 11
If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel.

3. Theorem 3-5
If two lines are cut by a transversal and alternate interior angles are congruent, then the lines are parallel.

4. Theorem 3-6
If two lines are cut by a transversal and same-side interior angles are supplementary, then the lines are parallel.

5. Theorem 3-7
In a plane two lines perpendicular to the same line are parallel.

6. Ways to Prove Two Lines Parallel
Show that a pair of corresponding angles are congruent.
Show that a pair of alternate interior angles are congruent.
Show that a pair of same-side interior angles are supplementary.
In a plane show that both lines are perpendicular to a third line.
Show that both lines are parallel to a third line.