Happy Tau Day!

[DGuller]

Yeah, but 1/2 * k * quantity squared is a very common form.  A lot of quantities that result from integration look like that.  Kinetic energy, for example.  It does seem like using pi is like using a QWERTY keyboard.

It's a common energy formula. I'm not sure why the area of a circle should look like an energy formula.

Both are outcomes of integration. 

[Maximus]

:hmmm: I'm not sure that's relevant. Many other things that don't look like energy formulae are also the outcomes of integration.