Pi R Squared

I had never seen this clever depiction of the proof that the area of a circle is Pi r squared.

This was published in the MIT alumni magazine as part of a discussion of clever teaching aids and I loved it. So I drew it up. While my grandkids are not yet ready to understand this one, I am collecting such attractive puzzles and proofs to share with them.

Since I had never seen it, I thought you two would like a preview.