# Hard Tweets Explained: No Pie for You

This may be my favorite tweet I’ve ever written. If not, it’s definitely up there in the top 314. This is the second post in an infinite series of posts in which I’ll explain my most difficult tweets. I’ll stop making that infinite series joke after this post, I promise.

The first thing you need to know is that there was a tweet meme going around of the form “The opening line of my life story would be…” So this is a play on that joke format.

The next thing you need to know is that I’m writing “pie” but meaning π. You remember π – that is the ratio of the circumference of a circle to its diameter. If you take your waist measurement, and then divide it by π, you get the exact length of the knife you’d need to commit harakiri.

π is an irrational number. That means that when you write it out 3.1415926535 (that’s all I know off the top of my head), it never repeats and it never ends. You might remember 22/7 as an approximation of π, but that is not terribly accurate. You can get more accurate by writing equations with lots and lots of fractions. The most famous of these was discovered by a fellow named Leibniz. It goes like this:

1 – ⅓ + ⅕ – ⅐ + ⅑ …

That actually doesn’t get you π, it gets you π/4. So you multiply that by 4 and you get π.

The sign is flipping back and forth +/- and the denominators (bottoms) of the fractions are all the odd numbers. Another way to write this is:

4 ∑ [(-1)ⁿ/(2n+1)]

That means 4 times the sum ( ∑ or “add this stuff up” ) of all the fractions with odd bottoms and sign-flipping tops. (There is a joke here about a sign-spinner wearing funny pants, but that is left as an exercise for the reader.) Maybe you should just trust me on how that equation gives you those fractions, because it’d take a couple more paragraphs to explain why that works.

So that’s the opening line of your life story if you really like pie – Leibniz’s equation for π.

The tweet then goes on to tell you that you aren’t going to get any pie.

This second bit is a joke about the nature of an infinite series. You can keep adding (and subtracting) smaller and smaller fractions in that equation and you get closer and closer to π. But you never actually get to π. You get really close. But never there.

So you never get to π – you never get any pie.

Homework: Go have some pie. Pair it with a nice wine, and toast Leibniz, who also invented calculus independently of Newton, but didn’t have as good a publicist. Apparently.