Example 13 and complete Your Turn #1-3 (adapted from Lesson 4.2). Angle Pair Relationships Same-Side Interior Angles Postulate - If two parallel lines are cut by a transversal, then the pairs of same-side interior angles are supplementary. Alternate Interior Angles Theorem - If two parallel lines are cut by a transversal, then the pairs of alternate interior angles have the same measure. Corresponding Angles Theorem - If two parallel lines are cut by a transversal, then the pairs of corresponding angles have the same measure. Suppose m21=140. Show how to find m25. m21=m45 by Corresponding Angles Theorem. Using the Substitution Property, substitute 140 for m21 to obtain m25 = 140. m21 = m25 140=m45 Corresponding Angles Theorem Substitution 2 Two parallel lines are cut by a transversal. Use Angle Pair Relationships to find m