Alternate Exterior Angles
In
the drawing below, angles 1 and 8 are alternate exterior angles,
as are angles 2 and 7. Alternate exterior angles are congruent.
Formally, alternate exterior angles are defined as two exterior
angles on opposite sides of a transversal which lie on different
parallel lines.
Parallel lines cut
by a transversal 

See
also
Alternate
interior angles,
consecutive interior angles
