Lesson 3.2: Angles and Parallel Lines
Key Concepts: Angles and Parallel Lines
Postulate and Theorems (when lines ARE parallel)
- Corresponding Angles Postulate: If two parallel lines are cut by a transversal, then corresponding angles are congruent.
- Alternate Interior Angles Theorem: If two parallel lines are cut by a transversal, then alternate interior angles are congruent.
- Alternate Exterior Angles Theorem: If two parallel lines are cut by a transversal, then alternate exterior angles are congruent.
- Consecutive Interior Angles Theorem: If two parallel lines are cut by a transversal, then consecutive interior angles are supplementary (sum to 180°).
Key Idea
When lines are parallel, the Angle relationships become predictable. These theorems are used extensively in proofs involving parallel lines.