Once the students have finished discovering that ALL triangles have three angles that add up to 180 degrees, they then investigate how many triangles are in each polygon. I created a quadrilateral, pentagon, hexagon, haxagon, heptagon, and octagon for them to investigate. They should arrive at teh conclusion that there is a pattern. The number of sides a polygon has minus 2 equals the number of triangles. They know that a triangle equals 180 degrees, so to figure out the sum of the interior angles, you just multiply the number of triangles by 180 degrees.
|Students started with a random triangle that they cut out. They|
labled and highlighted each angle.