Geometry
Ch. 4: Congruent Triangles
Investigate: Angle Sums in Triangles
Name: ___________________________________________________
Date: ____________________________________________________
Objective: To determine some relationships among the interior angles and exterior angles of a triangle.
Task 1: Interior Angle Sum
Step 1- Use a straight edge, draw and cut out a triangle. Label the
vertices 1, 2 and 3 as shown. These are called Interior Angles.
Step 2- Tear off the three corners of the triangle and place the interior
vertices next to each other.
Make a conjecture: What do you notice is formed by all three vertices together?
Write what you noticed as an If-then statement.
Try It Out! Given two angles, find the missing angle measure.
<a = _______________
Task 2: Exterior Angle Relationships
Step 1- Use a straight edge, draw a triangle. Extend one side long to create
an Exterior Angle (an angle outside the triangle) as shown in the diagram.
Label the vertices as shown and cut out the triangle.
Step 2- Tear off the Remote Interior Angles (<A and <B). Putting the two
vertices next to each other, use them to fill the Exterior Angle (<D).
Make a conjecture: What do you notice about the two Remote Interior Angles compared to the Exterior
Angle?
Write what you noticed as an If-then statement.Try it Out! Given the two remote interior angles, what will
the measure of the exterior angle be?