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ruveyn
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25 Jan 2013, 10:49 am

ianorlin wrote:
Vectorspace wrote:
I think the question was already correctly answered above. Just this:

Dividing "0 / 0" is "worse" than dividing, say "1 / 0".
In algebra, they say that dividing by 0 never makes sense in a field. It's just not defined.

You sometimes here people saying "well, if you divide by zero, you get infinity", which is not that wrong...
Even mathematicians sometimes define "1 / 0 = ∞". This is OK, if you know what you're doing.
The idea behind it is that you consider limits. The limit for "1 / x" with "x → 0" is ∞ if you require "x > 0" (otherwise, the limit doesn't exist).
You can do this, but you shouldn't be surprised that "1 / 0" and "2 / 0" are the same thing then (namely ∞). That's why you have to be careful when solving equations.

But "0 / 0" is worse. You can still try limits and consider "x / y" for "x → 0" and "y → 0" (with positive x,y). But then you still don't know... If you apply "x → 0" first, then the answer should be 0 (because any fraction with 0 in its nominator is 0). If you apply "y → 0" first, then the answer should be ∞.

tl;dr: Don't divide by zero. If you insist, don't be surprised about the implications.
You could use lohospital rule in the limit to find which approches zero if both are differentiable.


Provided one reaches k'th derivatives of the original functions for which division makes sense.

ruveyn



Thatmew
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25 Jan 2013, 11:06 am

I've thought of it like an infinite sheet of dough.

If you divide by zero, the sheet remains unchanged. Divide by one, and while it becomes whole, it is not the sum of the total infinite product.



ianorlin
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25 Jan 2013, 11:31 am

b9 wrote:
Quote:
0 divided by 0


nothing trumps infinity,
because nothing does not exist.

nothing's not something,
and something's not nothing,

there's no cosmological tryst,
twixt what is not and what is.


obviously infinity is not quantifiable (because it is larger than any brain that could inspect it fully), and zero is likewise unquantifiable (because it does not exist).


But the empty set is a subset of nothing because it is a subset of everything.



Trencher93
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25 Jan 2013, 12:01 pm

I'm glad people are thinking about this, even non-math people like YT. It's good to roll around ideas in your head and think about them. Most people tend to accept math as something inscrutable and with great authority.

When you divide by zero, there are only three realistic options. The answer could be 0, 1, or infinity. None works, which is why math leaves division by zero undefined. Notionally there are different ways to look at what it means to divide by nothing, but since none of the approaches actually works, it doesn't matter. (You could say division by zero is 0, because you've done nothing; you could also say it is 1, because you haven't divided anything; or you could say it's infinity because you have divided something as much as you can.)



ruveyn
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25 Jan 2013, 4:40 pm

Trencher93 wrote:
I'm glad people are thinking about this, even non-math people like YT. It's good to roll around ideas in your head and think about them. Most people tend to accept math as something inscrutable and with great authority.

When you divide by zero, there are only three realistic options. The answer could be 0, 1, or infinity. None works, which is why math leaves division by zero undefined. Notionally there are different ways to look at what it means to divide by nothing, but since none of the approaches actually works, it doesn't matter. (You could say division by zero is 0, because you've done nothing; you could also say it is 1, because you haven't divided anything; or you could say it's infinity because you have divided something as much as you can.)


Since 0 times any finite number is 0, 0 cannot have a multiplicative inverse (or reciprocal). So dividing by 0 is out, otherwise a contradiction would be introduced. That contradiction would be 0 = 1 which is just plain false.

ruveyn



MCalavera
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25 Jan 2013, 4:45 pm

Trencher93 wrote:
I guess Australian math is different, kind of like how water drains differently. :)


And all clocks here go counterclockwise, too.



ruveyn
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25 Jan 2013, 4:47 pm

MCalavera wrote:
Trencher93 wrote:
I guess Australian math is different, kind of like how water drains differently. :)


And all clocks here go counterclockwise, too.


Also the moon looks upside down in the Southern Hemisphere. That is because all you guys are hanging upside down.

ruveyn



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25 Jan 2013, 6:01 pm

Division by zero is a big no-no. Anyone who thinks 1/0 = ∞ has no understanding of infinity - it's much stranger than that. Look up HIlbert's Hotel for some interesting effects!

The reason 1/0 is undefined is because it's nonsense. Division is not a function in and of itself, but the inverse of another function (multiplication).
When we ask "what is x/y?" we are really asking "what is z where z*y=x?" For any value of y other than 0, there is an answer to this puzzle. What is 8/2? What is z when 2z=8? z=4. What is 1/0? What value is z when 0*z=1? There is no value for that. We all know that 0*z=0 for any z.



naturalplastic
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25 Jan 2013, 8:25 pm

Declension wrote:
Trencher93 wrote:
I guess Australian math is different


Actually, the entire Southern hemisphere was created when Abel Tasman accidentally divided by zero while doing calculations on his ship. True story!

This event released a powerful Anti-Logic Field which still lingers in the area to this day. It causes water to spin backwards and allows people to walk upside-down.


Absolutely!

In Australia you buy expensive and sell cheap in order to make a profit! And your boss will refuse to give you longer hours with less pay unless you go on strike!

They age backwards there too!



b9
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27 Jan 2013, 8:39 am

ianorlin wrote:
b9 wrote:
Quote:
0 divided by 0


nothing trumps infinity,
because nothing does not exist.

nothing's not something,
and something's not nothing,

there's no cosmological tryst,
twixt what is not and what is.


obviously infinity is not quantifiable (because it is larger than any brain that could inspect it fully), and zero is likewise unquantifiable (because it does not exist).


But the empty set is a subset of nothing because it is a subset of everything.

i understand what you mean.

in a strange way, everything is composed of nothing. it boggles quantitative arithmetic views of reality.

a "point" is a location of a singular element of space, and it has no volume because it has no dimensions on any axis. it therefore could be said that a point does not exist because it has zero size.

but the universal spacial volume is composed of individual points of space that can not be said to exist since they have zero volume.

in some ways i can conceive that it should take infinite acceleration to even depart from inertia considering that any velocity that starts at "zero" (with respect to the inertia of the subject at the beginning of the acceleration event) must make an infinite leap in velocity from "0 points per second" to "infinite points per second" before they can even be considered to be "moving"

the shortest distance that could ever be measured by the smartest life forms in the universe is nevertheless an infinite points long.

i can debate with mathematical knowledge i have (that i have learned from books), but i prefer to consider the ideas of "infinity" and "nothing" in a more philosophical sense. i do not want to enter an "i know more than you" altercation. i am not interested in academic debate. i never have been.
i am interested in personal considerations about the compilation of reality that are not strangled by peoples ideas that only the select few can ever think it through.


when i was young, i always wondered what was more powerful. infinity or nothing?
is an infinite amount of nothing bigger than a zero amount of everything?

i guess it is. an infinite amount of "nothing" produces "something" which is greater than the "nothing"
that is not multiplied infinitely.

a point multiplied by infinity (or given an infinite value) will give rise to a line, but a line does not exist either because it has no breadth or height. it only has length.

an infinite amount of lines are required to produce a plane which also does not exist. planes have no height so their volume is zero.

an infinite amount of planes are required to produce volume which does exist.

it is all composed of nothing however and that is the point.



Jono
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27 Jan 2013, 9:08 am

Thom_Fuleri wrote:
Division by zero is a big no-no. Anyone who thinks 1/0 = ∞ has no understanding of infinity - it's much stranger than that. Look up HIlbert's Hotel for some interesting effects!


I understand the concept fine. That actually does make sense in the context of limits but one must just not make the mistake of thinking that infinity is a multiplicative inverse, which it isn't.

Thom_Fuleri wrote:
What value is z when 0*z=1? There is no value for that. We all know that 0*z=0 for any z.


Consider the function f(z) = 1/z. Then lim(z -> ∞) f(z) = 0, lim(z -> ∞) z = ∞ and lim (z -> ∞) f(z)*z = 1.

One could also find functions where the form 0*∞ could approach any real number though. So algebraically, infinity cannot be a multiplicative inverse, nor can it have one.



Thom_Fuleri
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27 Jan 2013, 10:35 am

You do understand the concept, Jono - this is clear from your use of limits! Infinity is not a number but a concept - this is where most laypeople fall down, as they often think "infinity is the biggest possible number".



ruveyn
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27 Jan 2013, 12:36 pm

Thom_Fuleri wrote:
You do understand the concept, Jono - this is clear from your use of limits! Infinity is not a number but a concept - this is where most laypeople fall down, as they often think "infinity is the biggest possible number".


In the hyperreals infinity is a number (sort of) but it does not have the algebraic properties that standard real numbers have.

ruveyn



Jono
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27 Jan 2013, 2:10 pm

ruveyn wrote:
Thom_Fuleri wrote:
You do understand the concept, Jono - this is clear from your use of limits! Infinity is not a number but a concept - this is where most laypeople fall down, as they often think "infinity is the biggest possible number".


In the hyperreals infinity is a number (sort of) but it does not have the algebraic properties that standard real numbers have.

ruveyn


I'm not sure that there is a specific algebraic definition of "number". However, although it is possible to extend the set of real numbers to include infinite and infinitesimals, like what the hyperreals do, that set can no longer have algebraic properties required in order to be called a field.



Declension
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01 Feb 2013, 4:58 pm

Thom_Fuleri wrote:
Infinity is not a number but a concept - this is where most laypeople fall down, as they often think "infinity is the biggest possible number".


If you talk to laypeople like that, you'll just end up replacing one misconception with another. The honest answer is that the word "number" is not actually a technical term. It doesn't matter at all whether infinity is a "number" or not. What matters is that infinity is not in R (the "number line") but is in R-Bar (the "extended number line").



ruveyn
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01 Feb 2013, 7:59 pm

Straight from Euclid:

Σημεῖόν ἐστιν, οὗ μέρος οὐθέν.


ruveyn