If two parallel lines are intersected by a transversal,
then the consecutive interior angles are supplementary.
______________1 /2______________
3 / 4
/
__________ 5_/_6___________
7 / 8
1. / 1 and / 3 are a linear pair. 1. Definition of linear pair.
2. / 1 and / 3 are supplementary. 2. Linear pairs are supplementary.
3. / 1 + / 3 = 180. 3. Definition of supplementary.
4. / 1 = / 5 4. Corresponding Angles are equal.
5. / 5 + / 3 = 180 5. Substitution property.
6. / 5 and / 3 are supplementary. 6. Definition of Supplementary.