1. Proving Lines Parallel
Lesson 4 - 4
Proving Lines Parallel
Lesson 4-4: Proving Lines Parallel

2. Objective---What we’ll learn…
Prove two lines are parallel based on given angle relationships.
Lesson 4-4: Proving Lines Parallel

3. Proving Lines Parallel - Postulates & Theorems
If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel.
Lesson 4-4: Proving Lines Parallel

4. Proving Lines Parallel - Postulates &Theorems
If two lines are cut by a transversal and alternate interior angles are congruent, then the lines are parallel.
Lesson 4-4: Proving Lines Parallel

5. Proving Lines Parallel - Postulates &Theorems
If two lines are cut by a transversal and consecutive interior angles are supplementary, then the lines are parallel.
Lesson 4-4: Proving Lines Parallel

6. Proving Lines Parallel - Postulates &Theorems
If two lines are cut by a transversal and consecutive exterior angles are supplementary, then the lines are parallel.
Lesson 4-4: Proving Lines Parallel

7. Examples: Proving Lines Parallel
Find the value of x which will make lines a and lines b parallel. 2. 1. 3. 4.
Answers:
1. 20°
2. 50°
3. 90°
4. 20°
Lesson 4-4: Proving Lines Parallel

8. Ways to Prove Two Lines Parallel
Show that corresponding angles are equal.
Show that alternative interior angles are equal.
Show that consecutive interior angles are supplementary.
Show that consecutive exterior angles are supplementary.
In a plane, show that the lines are perpendicular to the same line.
Lesson 4-4: Proving Lines Parallel