ForumsWEPRCan we really trust math?

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Sssssnnaakke
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Sssssnnaakke
1,036 posts
Scribe

Ok I'm getting annoyed with people saying 0/0 is infinite. Zero groups of nothing equals well nothing. Yes on a graph it is -infinite and +infinite because how would you graph nothing? Or people saying that anything times zero equals so 0/0 can't be true. Because 0/0= (0)(x)=0. Well explain this then. If 0x1=0 and 0x2=0 then does 1=2?

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lightcrux
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lightcrux
622 posts
Peasant

x*(1/x)=? as x approaches 0.
From here it's important to note that 1/x as x approaches 0 = infinity.
thus the equation becomes x*infinity=? as x approaches 0


Quite true, but that is a solvable case:

Let, f(x)= x*(1/x)
As, x-->0, the limit of f(x) approaches 1.

Division by zero


As for division by zero that is an indeterminate case. Additionally, zero has infinitely many factors.


If 0x1=0 and 0x2=0 then does 1=2?


This is a bit hard for me to word but...

Note that both equations are equivalent. Thus, 0*1=0*2=0 but it does not imply 1 != 2, since such factorisation cannot be performed on zero.
NoNameC68
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NoNameC68
5,043 posts
Shepherd

0 can be treated as infinite yes. Infinity is the highest number possible. 0 by any number is 0 so in this sense it's treated as infinite (the highest number possible).


Well, infinity is the highest number impossible. ; )

I've never heard anyone refer to 0 as being infinite.

Wait, everyone here is aware that 1 = 0.999..., right?
qwerty1011
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qwerty1011
554 posts
Peasant

Look, the way multiplication works is that in xy you have x groups of y. If you have 0 groups you have 0. That is called logic. It means that however many groups of nothing you have it is still nothing. It doesn't mean if 1x0=0 and 2x0=0 then 1=2 because they are different numbers but it just doesn't matter when dividing by zero.

And dividing anything by 0 is infinite because there is an infinite amount of nothing in anything. I think though that because there is nothing in nothing 0/0=0.

But please don't ask this kind of question unless you understand how maths works because you clearly do not understand which makes your questions kind of stupid.

Armed_Blade
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Armed_Blade
1,482 posts
Shepherd

Wait, everyone here is aware that 1 = 0.999..., right?
Was that a joke?

Note that both equations are equivalent. Thus, 0*1=0*2=0 but it does not imply 1 != 2, since such factorisation cannot be performed on zero.


You're using the transitive property. In the last math book I had, the transitive property said it did not apply to cases of zero.
zakyman
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zakyman
1,627 posts
Peasant

Dividing anything by zero is undefined, not infinity. If I had 5 cookies, and I split them up into 0 groups, then I could not have 5 cookies if there were no groups. On the other hand, if it is infinit, than I will be very happy dividing my chocolate-peanut butter cookies by 0.

MageGrayWolf
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MageGrayWolf
9,462 posts
Farmer

Isn't infinity also undefined? As far as I can tell we are all correct. 0/0 is indeterminate, it is undefined, and it is infinite.

Sonatavarius
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Sonatavarius
1,322 posts
Farmer

i've only seen certain models use "any number excluding zero" / 0 as being infinity... i've yet to see it used as 0/0 as infinity in a class room... i've only ever seen a pure math course use it as indeterminate... or no solution.

Moegreche
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Moegreche
3,826 posts
Duke

You know, one of the classical problems of dealing with 0 is that we use it to define other sets - or at least we have in the past (some systems don't do this, but I don't know much about these systems).
So by giving a definition of 0 (perhaps as the empty set, or using the identity function) we can then define the successor function (plus '+' to independently derive other sets (numbers).
This gets complicated when we try to define more sophisticated function, like multiplication and division. But this reason alone isn't enough for us to not "trust math."
There may, however, be good reason to view math for what it is - an accepted logical system that can take certain inputs and give appropriate outputs. But of course any arithmetical system we have is also incomplete: there will be statements in that system that are not provable within the system. This is an extremely problematic result on the meta-level, but I don't think it's enough to reject arithmetic.

Programpro
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Programpro
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Nomad

Isn't infinity also undefined? As far as I can tell we are all correct. 0/0 is indeterminate, it is undefined, and it is infinite.


Infinity is defined as a number that permanently increases. It is not undefined. Undefined is a nonexistant or indeterminable number.

0/0 is undefined.

Technically, any real number divided by zero is undefined. You can't divide by zero.

Infinity is a concept used for limits. The limit of a positive number being divided by an approaching-zero number IS infinity. In fact, by L'Hopital's rule we can often find the limit of two divided numbers that are approaching zero, and it can be a finite number. But in any case, limits aren't real numbers, so really this paragraph is just a random math discussion I guess :P
indie55
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indie55
608 posts
Nomad

.9 repeating is 1.

zakyman
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zakyman
1,627 posts
Peasant

It's true lol

zakyman
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zakyman
1,627 posts
Peasant

Sorry for the double post but I wanted to add a proof.

If 1/3 is congruent to .3 repeating, and 1/3+1/3+1/3=1, then .3 repeating plus .3 repeating plus .3 repeating must also equal one. Also, find a number between .9 repeating and 1...I'll give you a hint, there isn't one.

Programpro
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Programpro
562 posts
Nomad

Sorry for the double post but I wanted to add a proof.

If 1/3 is congruent to .3 repeating, and 1/3+1/3+1/3=1, then .3 repeating plus .3 repeating plus .3 repeating must also equal one. Also, find a number between .9 repeating and 1...I'll give you a hint, there isn't one.


Or, the equally-cool algebraic proof:

let x = .99999999... forever

Now, consider the following:
10x - x = 9x

10x must be 9.999999..., and x is .999999..., so:

9.99999... - .99999... = 9x
9 = 9x
1 = x

But, x = .999999..., so therefore:

.99999.... = 1

QED
indie55
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indie55
608 posts
Nomad

For people who don't see the logic in that there are also many webpages devoted to it.

Sonatavarius
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Sonatavarius
1,322 posts
Farmer

another fun thing you might wanna watch out for...

1/3 = 0.3333333333333333333333333333333333...
2/3 = 0.6666666666666666666666666666666666...
3/3 = 1...and not 0.99999999999999999999999999999999...

i think someone else briefly alluded to this earlier.

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