There is a growing movement in certain math circles towards the opinion that π (pi) is wrong. Which is to say, it is the wrong number to be using and we would be better off using a symbol which means 2π, with the current candidate being τ (tau). Don't let this boring abstract put you to sleep; there are fun, informative videos within. Go watch them prove quite handily that π is a problem.
As you may or may not know, when C is the circumference of a circle and d is its diameter, which means that π (pi) is defined as the circumference of a circle divided by its diameter. This always comes out to 3.14 etc. Now, if we multiply each side of our definition of π by the diameter (which is two radii long) we end up with which looks very familiar. This is because it's the circumference formula! In other words, the circumference of a circle is 2· π· r. This seems okay, but when the math starts getting more complicated it becomes quite unpleasant. We need a new perspective. How about one where which means tau (τ) is defined as the circumference of a circle divided by its radius. The upshot is that and thus which makes sense, as now, for a unit circle (defined as a circle with a radius of 1), the circumference is 1τ instead of 2π. It also makes a bunch of other trigonometry a whole lot simpler and more intuitive.
Maybe I'm not explaining this very clearly. I'll let some experts do the job for me.