Only if the lines cut by the transversal are parallel.
they are angles that are usually parallel and that crossed the line that are oppsite from each other
Two angles that are congruent to each other and are on opposite sides of the parellel lines
When two parallel lines are cut by a transversal, the two pairs of angles on opposite sides of the transversal and outside the parallel lines, and the angles in each pair are congruent.
Both alternate interior and alternate exterior angle pairs lie on opposite sides of the transversal.