Unit 3 Lesson 5 Parallel Lines and Triangles
Unit 3, Lesson 5: Parallel Lines and Triangles
Lesson Overview
180... Always!
What You Will Learn
- how you can universally rearrange the corners of the triangle to form a straight angle.
- The sum of the angle measures of a triangle is always the same.
Additional Resources
Overview
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 essential theorem about triangles. To prove this theorem, you will need to use parallel lines.
This course is based on a textbook that is viewable by clicking on the textbook icon. Keep the textbook open while you go through the lesson so that you may refer to it throughout the lesson.
Additional Resources
Proceed to the Next Page
Prepare for Application
Instructions
You have now studied Reasoning in Algebra and Geometry. It is now time to demonstrate your learning.
Try the activities below on your own. You should be able to answer these before beginning the practice.
Do these activities in your journal.
Activity 1
Two angles of a triangle measure 53°. What are the exterior angle measures at each vertex of the triangle?
Activity 2
In the diagram below, what is the value of z?
Activity 3
Refer to problem three on page 174. Can you find without using the Triangle Exterior Angle Theorem? Explain.