# Interior Angles: Triangles

- Author:
- Mark Brouwer

## The interior angles of a triangle sum to two right angles

The objective of this activity is to understand WHY the interior angles of a triangle sum to two right angles

## Make a Construction

Create a triangle as the intersection of three lines: AB, BC, AC (plot three points on the plane and connect them with *lines* --not segments). Create a line parallel to AB through point C. Label points on each of the lines extending beyond the triangle, like this:

## Measure Angles

Please measure angles using the angle measurement tool. Please measure only the interior angles of ABC. Modify the color of each angle so that they are all different.