# Sum of a Triangle's Angles

- Author:
- Ms. Espy

- Topic:
- Angles

## Proving the Sum

__Rotate Triangle CDE__180 degrees around the midpoint of EC.

__Rotate__

__Triangle CDE__180 degrees around the midpoint of ED.

## Question 1: Proving the Sum Part 2

__Explain on your paper__ how these rotations prove that the sum of the angles in Triangle CDE is 180 degrees.

## Question 2: Finding the Missing Angles

__Find the measure__of the yellow angle below.

## Finding Missing Angles

## Question 3: Angle Relationships

__Extend the sides__of Triangle CDE above by using the Line tool.

__Redraw this figure__on your paper and

__fill in the measures__of

**all**missing angles.