When two parallel lines are cut …

Each of the parallel lines cut by the transversal has 4 angles surrounding the intersection. These are matched in measure and position with a counterpart at the other parallel line. At each of the parallel lines, there are two pairs of vertical angle. Each angle in the pair is congruent to the other angle in the pair. 1 4, angle 1 is congruent to angle 4. 2 3, angle 2 is congruent to angle 3. 5 8, angle 5 is congruent to angle 8. 6 7, angle 6 is congruent to angle 7. Adjacent Supplementary Angles At each of the parallel lines adjacent angles are supplementary. Names for the Matched Angles The angles have special names identifying their positions with respect to the parallel lines and transversal. They are corresponding angles, alternate interior angles, or alternate exterior angles. An angles is congruent to its matched angle.