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A transversal is a line, or line segment, that intersects two or more other lines, or line segments. When a transversal intersects parallel lines, many angles are congruent. Let's take a peek at what this means. Line segments k and j are parallel. Line segment l is a transversal.
As we mentioned before, when this happens we get a bunch of pairs of congruent angles. Remember: these angles are only congruent when the two lines crossed by the transversal are parallel. These pairs have nifty vocabulary terms to go with them. Here they are:
There are other pairs of angles in a transversal that aren't congruent but they do complete each other like peanut butter completes jelly. These are pairs of supplementary angles, meaning they add up to 180°, and they have their own peachy names. Again, these pairs of angles are only supplementary if the two lines crossed by the transversal are parallel. They are:
Look Out: these pairs of angles are congruent or supplementary only when the transversal cuts parallel lines.