Uses triangles to visualize circle's area as 兀r² As triangles get skinnier and skinnier, approximation to circle's area gets better, showing rectangle made of the same triangles. The rectangle shows area as r times r times pi (兀). Makes a triangle, square, hexagon, and all regular polygons (all made up of triangles). As number of sides of polygon increases, approximates circle. Draws to the right the same angles, like skinnier and skinnier pie slices, alternating to form a rectangle. That rectangle has one side that is 兀 times larger than the other side.
On left, 90 degrees yields a square, 60 degrees results in a hexagon, and so on, closer and closer to a circle. On right, shows the same pie slices on right stacked up as rectangle. Eventually, length approximate 兀r and the width is r. So circle's area = 兀r²
