Proving Lines Parallel - Postulates & Theorems l If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel. Lesson 2 -5: Proving Lines Parallel 2

Proving Lines Parallel - Postulates &Theorems l If two lines are cut by a transversal and alternate interior angles are congruent, then the lines are parallel. Lesson 2 -5: Proving Lines Parallel 3

Proving Lines Parallel - Postulates &Theorems l If two lines are cut by a transversal and same-side interior angles are supplementary, then the lines are parallel. Lesson 2 -5: Proving Lines Parallel 4

Proving Lines Parallel - Postulates &Theorems l If two lines are cut by a transversal and same-side exterior angles are supplementary, then the lines are parallel. Lesson 2 -5: Proving Lines Parallel 5

Examples: Proving Lines Parallel Find the value of x which will make lines a and lines b parallel. 2. 1. l 3. 4. Answers: 1. 20° 2. 50° 3. 90° 4. 20° Lesson 2 -5: Proving Lines Parallel 6

Ways to Prove Two Lines Parallel l l Show that corresponding angles are equal. Show that alternate interior angles are equal. Show that same-side interior angles are supplementary. Show that same-side exterior angles are supplementary. In a plane, show that the lines are perpendicular to the same line. Lesson 2 -5: Proving Lines Parallel 7