When parallel lines are cut by a transversal, several angle relationships occur. Corresponding angles are equal (e.g., if one angle is at the top - left of a transversal - intersection with one parallel line, the corresponding angle at the same relative position with the other parallel line is equal). Alternate interior angles are equal (angles between the parallel lines, on opposite sides of the transversal). Alternate exterior angles are equal (angles outside the parallel lines, on opposite sides of the transversal). Also, consecutive interior angles are supplementary (their sum is \(180^{\circ}\)). Vertical angles (opposite angles formed by the intersection of two lines, here the transversal and each parallel line) are equal too.