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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

One of my lecturers is doing a competition on the last day before the Christmas holidays to see what we think the best result is. All the students email him with the result that they think is best and then he announces the winner in the last lecture, and it'll be a nice, fun, wind-down-before-Christmas thingy.

In his opinion, the best result is that π/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - ...

However, I suspect that the winner of his competition will probably be that e^iπ + 1 = 0, not necessarily because it is the best result ever, but because it is a fairly well-known one and so more people will email that one to him because more people will know it. I mean, it is a fairly interesting result, how you can combine 3 seemingly unrelated numbers, 2 of which are transcendental and one of which is imaginary, together and get such a nice result. But I also think it's possible that there's a better one out there.

So I thought I'd post here to see if anyone knows some stuff that could possibly knock the ones above off their podiums. So if you know any really corking results, please do share!

(I think that 'results' is ambiguous intentionally, so that you can say anything that's at all maths-related.)

Edit: I'm just putting this here because it's not really worth a new post. Anyway, if you watched the 2006 Christmas Lectures then you might have seen the amazingly chaotic double-pendulum, which belongs to none other than the same lecturer that did this thing. Fun fact there.

Why did the vector cross the road?

It wanted to be normal.

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**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

you teach? (edit) whoops sorry, I read that too fast.

*Last edited by mikau (2006-12-07 15:33:34)*

A logarithm is just a misspelled algorithm.

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

No, I don't teach. Well, not officially anyway. You might say that helping out here counts as teaching, maybe.

Why did the vector cross the road?

It wanted to be normal.

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**Patrick****Real Member**- Registered: 2006-02-24
- Posts: 1,005

Ah, I can see why people would choose

. It's just that awesome, good job Euler :]*Last edited by Patrick (2006-12-08 07:59:31)*

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**Ricky****Moderator**- Registered: 2005-12-04
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I mean, it is a fairly interesting result, how you can combine 3 seemingly unrelated numbers, 2 of which are transcendental and one of which is imaginary, together and get such a nice result. But I also think it's possible that there's a better one out there.

Three? That equation contains the five most important numbers in math. 0 and 1 are two of the most important numbers, and as it turns out, pretty much as soon as you define 0 and 1, you define all of the real numbers.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**Zhylliolom****Real Member**- Registered: 2005-09-05
- Posts: 412

I must say

is my favorite as well, it is just so beautiful, displaying 5 of the most important numbers in mathematics, addition, multiplication, exponentiation, and equivalence. Also it is quite simple, which is a main factor in it being well-known.

Other results I am particularly fond of are

and

(of course taking the second expression too literally will give rise to dispute; it is actually an asymptotic relation)

Also the fact that

which shows that i[sup]i[/sup] is in fact a real number, is quite astonishing.

I enjoy infinite sums as well, but usually none stick out significantly from the rest. Here is *Zhylliolom's identity* for φ (please submit this one, don't forget to mention me ):

(actually, I need to rederive my identity to make sure it is actually correct here, so wait on that!)

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**Ricky****Moderator**- Registered: 2005-12-04
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Is that phi Euler's totient function? Certainly an interesting expansion if correct.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,569

Binet's Formula (phi is the Golden Ratio):

That a formula like that produces whole numbers is amazing enough, but **Fibonacci Numbers**?

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**Ricky****Moderator**- Registered: 2005-12-04
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Right, not sure what I was thinking. Of course it can't be the function phi, that takes a variable...

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**vipaman****Member**- Registered: 2006-09-30
- Posts: 22

Did not get it.help.

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**Patrick****Real Member**- Registered: 2006-02-24
- Posts: 1,005

What don't you get vipaman?

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**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

Ricky wrote:

pretty much as soon as you define 0 and 1, you define all of the real numbers.

wait... what? care to elaborate

The Beginning Of All Things To End.

The End Of All Things To Come.

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**Patrick****Real Member**- Registered: 2006-02-24
- Posts: 1,005

Also, which one won?

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**mathsyperson****Moderator**- Registered: 2005-06-22
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Ooh, I meant to post the results here but then forgot. Good bumping.

As I suspected, first place went to e^iπ + 1 = 0. But he also gave some runner-ups (or runners-up?), which were quite interesting.

In no particular order,

1.

2.

3.

That last summation I particularly liked because it was so complicated. And for every term in the series you add on, you get around another 8 decimal places of π, so it converges incredibly quickly.

Why did the vector cross the road?

It wanted to be normal.

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**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

for 1. you might also write it:

bad notation, but you know what i mean

*Last edited by luca-deltodesco (2007-01-11 10:36:08)*

The Beginning Of All Things To End.

The End Of All Things To Come.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

luca-deltodesco wrote:

Ricky wrote:pretty much as soon as you define 0 and 1, you define all of the real numbers.

wait... what? care to elaborate

I can certainly try.

Imagine we define what 0 and 1 are. These are the identity for addition and multiplication respectively. This simply means:

0 + a = a + 0 = a

and

1 * a = a * 1 = a

For all a in the "field" (a set with special properties). But from here on out, we won't call these numbers because it turns out that they don't have to be. The following will apply to anything with these properties (as well as a lot which haven't been mentioned). So we will call the additive identity (0) e, and the multiplicative identity (1) u.

Now we can define all the positive numbers, simply by adding up e's.

2 = e + e

3 = e + e + e

and so on...

Note that I use "2" and "3" here as symbols. All "2" stands for is the identity added with itself. "3" just means the identity added 3 times.

I now call all these things positive elements. I define negative numbers to be:

if a is positive, then -a is an element of F such that:

a + -a = e (0)

With numbers, this means 2 + -2 = 0. With a field (as the reals are defined), we are guaranteed that such elements exist. So now we have all the "integers".

Now we define elements 1/a to be such that:

a * 1/a = u

Again, in a field, we are guaranteed that such elements exist. We also define a/b to be:

a * 1/b

And now you'll notice that we get all the rationals. An offset of this is that u/e (1/0) does not exist, for various reasons.

Now we get to the reals and here is where things get complicated. The reals can be defined by sets of rational numbers, known as a Dedekind cut. However, it would take too much to explain how this works.

So hopefully it is a bit clear how we can define every single number with 0 and 1. I believe this can be done with 1 alone, but it requires a few little tricks, and I'm not sure if these tricks apply to all complete fields or not.

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**Ricky****Moderator**- Registered: 2005-12-04
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