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**Mathisweird****Member**- Registered: 2014-02-20
- Posts: 1

My issue is why 10x why not (infinite)x. The rule is multiply 10 by each number after the decimal point but if .9999 repeating then you multiply by infinite?

Infinite x - x = infinite -x

Infinite x = infinite

X= infinite/infinite = undefined

So if Infinite/infinite=1 then 0.99999=1

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

Hi;

why not (infinite)x.

What exactly does that mean? You can not say ∞ * x because infinity is not a number.

The rule is multiply 10 by each number after the decimal point

What rule?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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That would be a bad idea. ∞ is not a normal number.

Multiplying and dividing with ∞ will cripple all your equations.

For example,

x + 2 = 0

⇒ x = -2

If we tried t multiply and divide by ∞

x + 2 = 0

⇒ ∞(x + 2) = ∞ 0

⇒ ∞x + ∞ = Indeterminate

⇒ x = (Indeterminate-∞)/∞ = Indeterminate

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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Rule Dividing by ∞ is not allowed.

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,062

Agnishom wrote:

Rule Dividing by ∞ is not allowed.

from where did this rule come? we divide 1 by infinity in physics for solving some of the numericals in lens, as it is the far point of the eye.

friendship is tan 90°.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,000

You NEVER divide by infinity. More precisely, you NEVER use infinity as a number. What you do in physics class is look at the limit of the expression as one of the distances tends to infinity. You just use it intuitively without notation.

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Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,501

Mathisweird wrote:

So if Infinite/infinite=1 then 0.99999=1

All that about not treating infinity as a number plus this.

Why not:

So if Infinite/infinite=67.234 then 0.99999=67.234

and then 67.234 = 1 => 66.234 = 0 etc etc

Whoops. That's why you cannot treat infinity as a number.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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niharika_kumar wrote:

Agnishom wrote:Rule Dividing by ∞ is not allowed.

from where did this rule come? we divide 1 by infinity in physics for solving some of the numericals in lens, as it is the far point of the eye.

In the physics class, you also divide by 0 to get infinity but that is also finding the limit like stefy said

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

Some CAS also did that. I remember Mupad, can you guess who was instrumental in putting it into that CAS?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,648

From what I have read, operations on infinity depends on the person. For example, according to Rudin, all primitive operations on infinity are defined.

*Last edited by ShivamS (2014-02-21 14:00:09)*

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bobbym wrote:

Some CAS also did that. I remember Mupad, can you guess who was instrumental in putting it into that CAS?

Who? You? JaneFairFax? Anthony R Babbage?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

It was me of course.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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It is a bad idea

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

From the engineering point of view it saves time. But mathematically it is incorrect.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,062

oh, thanks.

friendship is tan 90°.

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'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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He is not GiB?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

This one is left open.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**Calligar****Member**- Registered: 2011-09-24
- Posts: 272

Is this the only topic (on this subject) still left open?

[edit] I'm adding this, because I should note I have no intention of bringing the argument back, I was just curious because everything else on the issue I found seemed to be closed.

*Last edited by Calligar (2016-01-01 13:02:32)*

There are always other variables. -[unknown]

But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end. -Aristotle

Everything makes sense, one only needs to figure out how. -[unknown]

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

Hi;

Yes, 1248 threads about the same thing is a bit much.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**Calligar****Member**- Registered: 2011-09-24
- Posts: 272

I've been reading through a lot of the old stuff (I haven't been on in a few years), I was surprised to see all those topics closed. I would like to argue how keeping it open for discussion can still be useful, but I won't do that on this topic.

There are always other variables. -[unknown]

But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end. -Aristotle

Everything makes sense, one only needs to figure out how. -[unknown]

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

I have nothing against a good argument but most of the arguments that were generated have been deleted. In particular it seemed to attract one big troll.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**Calligar****Member**- Registered: 2011-09-24
- Posts: 272

A troll? From what I was reading, it seemed like everybody was serious about what they thought (though a lot went unexplained and people from both sides were getting frustrated). Was it really all trolling? Hmm, should I make a new topic to discuss this, I'm afraid it'll take this topic off-topic?

There are always other variables. -[unknown]

But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end. -Aristotle

Everything makes sense, one only needs to figure out how. -[unknown]

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,304

All the abusive, vulgar material was deleted, with good reason. Why is it necessary to have more than one thread on this subject?

Was it really all trolling?

Please explain what you are implying.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**

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**Calligar****Member**- Registered: 2011-09-24
- Posts: 272

Okay, well the biggest issue I see is it typically comes down to two sides. 0.9... = 1, because the 9s infinitely repeat. It is because it infinitely repeats (trying to keep it simple w/o all the proofs), that you can't do anything to it and you use it to exactly be 1. A simple example (I think) is 1 divided by 3 = 0.3... If you multiply that by 3, you get 0.9... Therefore, it = 1. However, the other side sees it as a different number, and will try to fix it by working with the infinite 9s similar in a way where it seems finite. For instance 0.9... + 0.0...1 = 1, therefore 0.9...≠1. Now all this stuff has been said before, so no need to go into details, however, connecting all this to people who might be seen as trolling: when one side does not understand the other side, frustration occurs. People begin arguing they either aren't listening to one another, and begin to feel that the others are just repeating themselves. The problem occurs when people begin name calling and such as that creates basically an insulting game between the two. This can completely lose focus and lead to arguments between each other, spamming and other things. So my point in all of this, is was it really all trolling? Because couldn't it have simply been something that got out of hand?

Side Note: Sorry for bringing up old examples that were discussed before, I was only using them to make a point while trying to keep it simple.

But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end. -Aristotle

Everything makes sense, one only needs to figure out how. -[unknown]

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