3.1 Parallel Lines, Transversals, and Angle Pairs Warm-Up

Parallel lines are lines in a plane that never meet and are always the same distance apart.

A transversal is a line that intersects two or more lines at different points.

Vertical angles are the angles opposite each other when two lines intersect. They are always equal.

Alternate interior angles are pairs of angles on opposite sides of a transversal but inside the two lines. They are equal when the lines are parallel.

Corresponding angles are pairs of angles that are in the same position on two different lines cut by a transversal. They are equal when the lines are parallel.

Alternate exterior angles are pairs of angles on opposite sides of a transversal but outside the two lines. They are equal when the lines are parallel.

Consecutive interior angles are pairs of angles on the same side of the transversal and inside the two lines. They are supplementary when the lines are parallel.

When a transversal intersects parallel lines, specific angle pairs (corresponding, alternate interior, alternate exterior, and consecutive interior) have defined relationships (equal or supplementary).

Vertical angles can be identified as the angles that are opposite each other at the intersection of two lines.

Alternate interior angles can be identified as the angles that lie between the two lines and are on opposite sides of the transversal.