A Triangle's Angles

The sum of the measures of the interior angles of any triangle is 180°.

This is a Java Applet created using GeoGebra from www.geogebra.org - it looks like you don't have Java installed, please go to www.java.com

To reflect an object, make sure the "Reflect about Point" tool is selected.
Then click the object to reflect, followed by the point.

How does this show that the angles add up to 180°?
Can you use this to find a formula for the area of the triangle?

Steve Kifowit, Created with GeoGebra