# Proof without words: Twelve corners

Here we are again dealing with a *proof without words* and the *circular number .* What is the area of a *regular dodecagon* that has a circumcircle of *radius* ? The puzzle you have in front of you provides an answer in an amazingly simple way: Put the pieces together so that they form three squares of equal size with an edge length of one. Since *equality of content* follows from *equality of decomposition*, the area of the given dodecagon must be exactly . This is also close to the circle number , which is the area of the unit circle (and ).