A transversal is a line that intersects (or crosses) two parallel lines and makes eight angles.
Using a transversal, we can identify many types of angles: vertical angles, corresponding angles, interior angles, alternate interior angles, exterior angles, and alternate exterior angles. We use these angles to determine angle measures (because of congruency and complimentary/supplementary angles).
Vertical angles make a “bow-tie” shape. They reflect across a shared intersection and are congruent. An example of vertical angles would be the top angle and the bottom angle formed in the letter X (the right-side angle and the left-side angle are also vertical angles).
Corresponding angles are easy to find. These angles are in the “same place” in the sense that if you placed the intersections one on top of the other, they would be in the same place.
Interior Angles & Alternate Interior Angles
Interior angles are “in the road” formed by the two parallel lines. They are inside the two parallel lines.
Alternate interior angles are “in the road,” but are on opposite sides of the “road” and opposite sides of the cross-walk (transversal line).
Exterior Angles & Alternate Exterior Angles
Exterior angles are “on the sidewalk” or off the “road” formed by the two parallel lines. They are outside the parallel lines.
Alternate exterior angles are “on the sidewalk,” but are on opposite sides of the road and opposite sides of the “cross-walk” (transversal line).
Supplementary angles are angles that, when put together, add up to 180 °. Basically, the two angles put together make a straight angle, or a straight line.
Supplementary angles are used when working with transversals because they assist you in finding the angle measure of unknown angles (180° - known measure = missing measure)*
*This only works when the angles are supplementary angles!!!