Angles Involving Parallel Lines

http://www.regentsprep.org/Regents/math/geometry/GP8/Lparallel.htm

Linear Pair
If two angles form a linear pair, then the measures of the angles add up to 180°.

Vertical Angle
If two angles are vertical angles, then they have equal measures (are congruent).

Corresponding Angles
If two parallel lines are cut by a transversal, then corresponding angles are congruent.

Alternate Interior Angles
If two parallel lines are cut by a transversal, then alternate interior angles are congruent.

Alternate Exterior Angles
If two parallel lines are cut by a transversal, then alternate exterior angles are congruent.