News for hackers. Stuff that matters.
Re:Why can't we divide by zero? by marvin on Sunday September 28, 2008 @06:36PM (#317888)
I'm still not convinced that you can't just say that x/0 equals infinity. Certainly, infinity is not a number..but it has the same properties as a transcendental number in the sense that it is impossible to describe it accurately with finitely many digits. You wouldn't be able to use this definition to build other theories, but it would be nice to have a settled definition. Saying that x/0 is undefined still seems to me like a bit of a hack.

I agree that 0/0 should be undefined. There are infinitely many possibilities for what it could be, depending on the context.

Re:Why can't we divide by zero? by hhm on Sunday September 28, 2008 @07:07PM (#317904)
Infinity is a much studied concept in mathematics; the problem is not that we don't know what infinity is but that we know it's not part of the set of integer numbers, real numbers, etc. But there are many ways to work with infinities, and even to include it in the number sets (for example, in the case of hyper-reals).
Re:Why can't we divide by zero? by parenthesis on Sunday September 28, 2008 @07:49PM (#317922)
Re:Why can't we divide by zero? by hugh on Monday September 29, 2008 @03:44PM (#318720)
I'm still not convinced that you can't just say that x/0 equals infinity.

Certainly, there's nothing to stop you from saying that. We could quite easily define a number called Infinity (or, say, Frank) such that x/0 = Frank, the same way we defined a number i such that sqrt(-1) = i. People have thought about this for centuries, I'm sure, but the reason that it hasn't taken off the way i has is that positing the existence of "i" gets you a whole lot of new and useful mathematics (e.g. a new field of complex numbers which is closed under arbitrary roots) whereas positing the existence of Frank doesn't buy you much except trouble.

For instance, consider our new number system consisting of the reals plus Frank. We'll have to define operations on Frank now. Clearly, Frank + Frank = Frank and Frank * Frank = Frank. But what about Frank - Frank and Frank/Frank? You can't define them as 0 and 1 respectively, or else you find yourself with proofs like this:

Frank = Frank + Frank

Frank/Frank = Frank/Frank + Frank/Frank

1 = 2

which is undesirable. So you've still got undefined numbers in your number system, and your number system no longer has lots of the nice properties that you get when you have a field.

Also, Frank doesn't share all that many of the properties that are usually associated with what we now know about infinities -- e.g. the idea that there are "different sizes" of infinite sets which can't be mapped onto one another.

Re:Why can't we divide by zero? by michaelneale on Sunday September 28, 2008 @08:07PM (#317936)
>Certainly, infinity is not a number..but it has the same properties as a transcendental number in the sense that it is impossible to describe it accurately with finitely many digits.

But other transcendental numbers can be used like regular numbers - infinity can not, I thought? Or at least not as easily as those other numbers are.

Re:Why can't we divide by zero? by derefr on Sunday September 28, 2008 @07:42PM (#317916)
Is it at least true that (0 < |0/0| < Infinity); that is, that 0/0 is a finite, non-zero number?
Re:Why can't we divide by zero? by newt0311 on Sunday September 28, 2008 @07:58PM (#317928)
No. 0/0 is completely undefined. For example, consider limit as x approaches 0 of (-x)/x. This approaches (-0)/0 = 0/0 but simplifying the limit given an answer of -1. So 0/0 is completely dependent on the characteristics of the convergence and had no meaning in isolation. In fact, the field of real (and complex) numbers does not even include 0 in the multiplicative group. Therefore, dividing by 0 is nonsensical as it has no inverse as it is not in the multiplicative field. According to the basic axioms of groups theory, given a field F with a the identity of the additive group in the field and b some element of the multiplicative group, it can be proven that mul(a,b) = a where mul is the multiplication operation. This explains why 0 times any other number is 0. If you would like a copy of the proof, just drop me an email.

Sorry for the rant, math major.

Re:Why can't we divide by zero? by cheese825 on Monday September 29, 2008 @12:15AM (#318092)
I'd love to see the proof. But you did not post your email address. Could you send it to mine?
Re:Why can't we divide by zero? by newt0311 on Monday September 29, 2008 @04:11AM (#318202)
oops. Sorry about that. Fixed.

PS. Your email address is not posted either.

Re:Why can't we divide by zero? by hhm on Monday September 29, 2008 @09:45AM (#318324)
Isn't it something like this?

0=a-a, for all a

(where a-a is actually, a+(-a))

so: mul(b,0)=mul(b,(a-a))=mul(b,a)-mul(b,a)=z-z=0

Re:Why can't we divide by zero? by newt0311 on Monday September 29, 2008 @10:04AM (#318343)
pretty much.