If two lines are cut by a transversal so that the interior angles on the same side of the transversal are supplementary, then these lines are parallel

Given: Lines n and m; transversal t



Prove:
m||n





Proof:

- Given
- If the exterior sides of two adjacent angles form a straight line, these angles are supplementary

- If two angles are supplementary  to the same angle , they are congruent

m||n - If two lines (m, n) are cut by a transversal (t) so that the corresponding angles (1, 2) are congruent, then these lines are parallel