More angle relationships with parallel lines: alternate interior and alternate exterior angles

Some more terminology to learn... alternate interior angles are on the "inside" in relation to the two parallel lines, and they alternate, in relation to the transversal. Alternate interior angles are congruent. And similarly for alternate exterior angles, they're on the exterior in relation to the parallel lines, and alternate in relation to the transversal, and are congruent. Nothing new mathematically here, really, because you can know they are congruent even without knowing the terminology (by using the facts that vertical angles are congruent and that corresponding angles are congruent).

See also

Review of basic angle relationships — video lesson

Math Mammoth Grade 8 curriculum

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