3-5 Parallel Lines and Triangles

Objectives

To use parallel lines to prove a theorem about triangles

To find measures of angles of triangles

A Solve It problem demonstrates angles of a triangle.
Image Long Description

In the Solve It, you may have discovered that you can rearrange the corners of the triangle to form a straight angle. You can do this for any triangle.

Essential Understanding The sum of the angle measures of a triangle is always the same.

The Solve It suggests an important theorem about triangles. To prove this theorem, you will need to use parallel lines.


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Table of Contents

Prentice Hall Geometry Chapter 1 Tools of Geometry Chapter 2 Reasoning and Proof Chapter 3 Parallel and Perpendicular Lines Chapter 4 Congruent Triangles Chapter 5 Relationships Within Triangles Chapter 6 Polygons and Quadrilaterals Chapter 7 Similarity Chapter 8 Right Triangles and Trigonometry Chapter 9 Transformations Chapter 10 Area Chapter 11 Surface Area and Volume Chapter 12 Circles Skills Handbook Reference Visual Glossary Selected Answers Index Acknowledgments