## Angle Sum of a Triangle

The sum of the three interior angles in a triangle is 180°.

An

A

An

**informal**way of proving this statement is to do the following activity:- Draw a large triangle on a piece of paper (use a ruler to make sure your lines are straight)
- Cut out the triangle
- Tear off each of the three corners
- Line the three corners up against your ruler to show that they add to a straight line (180°)

A

**formal**way of proving this statement is to do the following activity:(12)