Transversal
In geometry, a transversal is a line that passes through two lines in the same plane at different points. When the lines are parallel, as is often the case, a transversal produces several congruent and several supplementary angles. When three lines in general position that form a triangle are cut by a transversal, the lengths of the six resulting segments satisfy Menelaus' theorem.
Terminology
When a line t is the transversal of two lines a and b there are a total of eight angles formed. Names have been given to these angles and specific pairs. There are four interior angles defined as angles between a and b, and the remaining four are called exterior angles. A pair of angles, one formed by t and a and the other formed by t and b, are called corresponding angles if they are on the same side of t and on the same sides of a and b respectively. Similarly, a pair of angles are called alternating angles if they are on opposite sides of T and opposite sides of a and b.
Alternate exterior angles created by a transversal of two lines.
Alternate interior angles created by a transversal of two lines.
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