Parallel Lines and Transversals
Theorem. Same-Side Exterior Angles Theorem
If two parallel lines are cut by a transversal, then the exterior angles on the same side of the transversal are supplementary
Prove this theorem as an exercise.
Another way of proving the Triangle Angle-Sum Theorem is by applying the postulate and theorems about the properties of angle pairs of parallel lines cut by a transversal.
Example
Prove the Triangle Angle-Sum Theorem, stating that the sum of the measures of the interior angles of any triangle is always
Solution
| Given: | with interior angles and |
| Prove: |
Proof:
