1. WHAT is the relationship
among the measures of the
angles of a triangle?
Course 3, Inquiry Lab before Lesson 5-3
Geometry

2. • 8.G.5
Use informal arguments to establish facts about the angle sum and
exterior angle of triangles, about the angles created when parallel lines
are cut by a transversal, and the angle-angle criterion for similarity of
triangles.
Mathematical Practices
1 Make sense of problems and persevere in solving them.
3 Construct viable arguments and critique the reasoning of others.
Course 3, Inquiry Lab before Lesson 5-3 Common Core State Standards © Copyright 2010. National Governors Association Center for
Best Practices and Council of Chief State School Officers. All rights reserved.
Geometry

3. Course 3, Inquiry Lab before Lesson 5-3
Activity
continued

Geometry
Triangle means three angles. In this Activity you will explore
how the three angles of a triangle are related.
On a separate piece of paper, draw a triangle like the one
shown below.

4. Course 3, Inquiry Lab before Lesson 5-3
Activity
continued

Geometry
Triangle means three angles. In this Activity you will explore
how the three angles of a triangle are related.
Label the corners 1, 2, and 3. then tear off each corner.

5. Course 3, Inquiry Lab before Lesson 5-3
Geometry
Triangle means three angles. In this Activity you will explore
how the three angles of a triangle are related.
Rearrange the torn pieces so that the corners all meet at
one point. Label the torn pieces with 1, 2, and 3.
What does each torn corner represent?
_____________________________________________
The point where these corners meet is the vertex of another angle.
Classify the angle as acute, right, obtuse, or straight. Explain.
______________________________________________________

6. Course 3, Inquiry Lab before Lesson 5-3
WHAT is the relationship
among the measures of the
angles of a triangle?
Geometry