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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: 92,228

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.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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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'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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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'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,031

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: The Foundation
- Registered: 2011-05-23
- Posts: 15,821

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.

Here lies the reader who will never open this book. He is forever dead.

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: 6,732

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

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'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,228

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.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,640

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'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,228

It was me of course.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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It is a bad idea

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

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,228

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.**

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**niharika_kumar****Member**- From: Numeraland
- Registered: 2013-02-12
- Posts: 1,031

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'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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He is not GiB?

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

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 92,228

This one is left open.

**In mathematics, you don't understand things. You just get used to them.**

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