Previously:

**What Only One Person Ever Has Thought ‘Pi’ Means, And Who That Was****As I Try To Figure Out What Wronski Thought ‘Pi’ Was****Deciphering Wronski, Non-Standardly****As I Try To Make Wronski’s Formula For Pi Into Something I Like****Wronski’s Formula For Pi: A First Limit****Wronski’s Formula For Pi: Two Weird Tricks For Limits That Mathematicians Keep Using****Wronski’s Formula For Pi: How Close We Came**

So, I must confess failure. Not about deciphering Józef Maria Hoëne-Wronski’s attempted definition of π. He’d tried this crazy method throwing a lot of infinities and roots of infinities and imaginary numbers together. I believe I translated it into the language of modern mathematics fairly. And my failure is not that I found the formula actually described the number -½π.

Oh, I had an error in there, yes. And I’d found where it was. It was all the way back in the essay which first converted Wronski’s formula into something respectable. It was a small error, first appearing in the last formula of that essay and never corrected from there. This reinforces my suspicion that when normal people see formulas they mostly look at them to confirm there is a formula there. With luck they carry on and read the sentences around them.

My failure is I wanted to write a bit about boring mistakes. The kinds which you make all the time while doing mathematics work, but which you don’t worry about. Dropped signs. Constants which aren’t divided out, or which get multiplied in incorrectly. Stuff like this which you only detect because you know, deep down, that you should have gotten to an attractive simple formula and you haven’t. Mistakes which are tiresome to make, but never make you wonder if you’re in the wrong job.

The trouble is I can’t think of how to make an essay of that. We don’t tend to rate little mistakes like the wrong sign or the wrong multiple or a boring unnecessary added constant as important. This is because they’re not. The interesting stuff in a mathematical formula is usually the stuff representing variations. Change is interesting. The direction of the change? Eh, nice to know. A swapped plus or minus sign alters your understanding of the direction of the change, but that’s all. Multiplying or dividing by a constant wrongly changes your understanding of the size of the change. But that doesn’t alter what the change looks like. Just the scale of the change. Adding or subtracting the wrong constant alters what you think the change is varying from, but not what the shape of the change is. Once more, not a big deal.

But you also know that instinctively, or at least you get it from seeing how it’s worth one or two points on an exam to write -sin where you mean +sin. Or how if you ask the instructor in class about that 2 where a ½ should be, she’ll say, “Oh, yeah, you’re right” and do a hurried bit of erasing before going on.

Thus my failure: I don’t know what to say about boring mistakes that has any insight.

For the record here’s where I got things wrong. I was creating a function, named ‘f’ and using as a variable ‘x’, to represent Wronski’s formula. I’d gotten to this point:

And then I observed how the stuff in curly braces there is “one of those magic tricks that mathematicians know because they see it all the time”. And I wanted to call in this formula, correctly:

So here’s where I went wrong. I took the way off in the front of that first formula and combined it with the stuff in braces to make 2 times a sine of some stuff. I apologize for this. I must have been writing stuff out faster than I was thinking about it. If I had thought, I would have gone through this intermediate step:

Because with *that* form in mind, it’s easy to take the stuff in curled braces and the in the denominator. From that we get, correctly, . And then the on the far left of that expression and the on the right multiply together to produce the number 8.

So the function *ought* to have been, all along:

Not very different, is it? Ah, but it makes a huge difference. Carry through with all the L’Hôpital’s Rule stuff described in previous essays. All the complicated formula work is the same. There’s a different number hanging off the front, waiting to multiply in. That’s all. And what you find, redoing all the work but using this corrected function, is that Wronski’s original mess —

— should indeed equal:

All right, there’s an extra factor of 2 here. And I don’t think *that* is my mistake. Or if it is, other people come to the same mistake without my prompting.

Possibly the book I drew this from misquoted Wronski. It’s at least as good to have a formula for 2π as it is to have one for π. Or Wronski had a mistake in his original formula, and had a constant multiplied out front which he didn’t want. It happens to us all.

Fin.

That’s a charming post – and comforting in a sense! Always when I am close to hit Publish on a post that includes derivations I cooked up on my own I live in fear that I made a mistake :-) … especially when the result was ‘beautiful’.

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Aw, thank you. How nervous I get before posting something depends on just how much of my own derivations (or proofs) run in it, especially if I can’t find it done by someone else somewhere. It just feels ridiculous to suppose that I might be both original and correct. I feel lucky there’s not more people writing in to tell me where it all went wrong.

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If it wasn’t for boring mistakes, Niels Bohr wouldn’t get any shout outs at all.

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Oh, no, he’d get in on some of that great kneeling action too.

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