Read a more complete explanation here: http://pythagoreanmath.com/complete-explanation-for-area-of-a-circle-formula/ pi;r(squared) gives you the area of a circle, but where does it come from? Here is a simple explanation. Reddit discussion about the video here: https://www.reddit.com/r/pythagoreanmath/comments/5wt8ow/area_of_a_circle_video/