1. Parallel Lines and Triangles Chapter 3 Section 5

2. Objective Students will use parallel lines to prove a theorem about triangles. Students will find measures of angles of triangles.

3. Postulate 3-3 Parallel Postulate Through a point not on a line, there is one and only one line parallel to the given line.

4. Theorem 3-10 Triangle Angle-Sum Theorem The sum of the measures of the angles of a triangle is 180.

5. Auxiliary Line A line that you add to a diagram to help explain relationships in proofs.

6. Page 172 in the textbook Look at the proof at the bottom of page 172. Try the “Got It” for Problem 1 on page 173.

7. Exterior Angle An angle formed by a side and an extension of an adjacent side.

8. Remote Interior Angle Angles on the interior of a figure that are non-adjacent to the exterior angle.

9. Theorem 3-11 Triangle Exterior Angle Theorem The measure of each exterior angle of a triangle equals the sum of the measures of its two remote interior angles.

10. Turn to Page 174 in the textbook. Look at problem 2 and 3. Try the “Got It” problem for both examples.

11. On page 175 in the textbook Try problems #1-8.