Is There a Shorter Proof for 0.999... = 1?

[eNathan]

J33Z these threads are always poping up, well I think this thread was pulled up from a while ago but...

This is my conclusion
1 - .999~ = 000 \infty
To say that 1 != .999\infty is to say that x * 000\infty!= 0

Sorry I forgot the latex code for <> or !=, what is it again

 

[yourdadonapogostick]

\infty is undefined, so i would have to say that is completely wrong

 

[rachmaninoff]

\infty is undefined, so i would have to say that is completely wrong

Well, he is completely wrong, but \infty is well-defined (you're wrong about that), but arithmetic on \infty is not, so \infty \cdot 0 is what's undefined.

 

[Zurtex]

J33Z these threads are always poping up, well I think this thread was pulled up from a while ago but...

This is my conclusion
1 - .999~ = 000 \infty
To say that 1 != .999\infty is to say that x * 000\infty!= 0

Sorry I forgot the latex code for <> or !=, what is it again

Your looking for \neq

Would you like to make any mathematical sense of that? Or should I not bother asking?

 

[eNathan]

Your looking for \neq

Would you like to make any mathematical sense of that? Or should I not bother asking?

here we go again

if you were to perform the following operation

1 - .9 you would get .1

if you were to do
1 - .9999999999 you would get .0000000001

Now if you were to manually try to subtract .999 \infty from 1, you would get 000000000 for infintiy! hence,
1 - .999 \infty = 000 \infty Make sense? So to say that 1 - .999 \infty \neq 0 would also mean that that the infinite row of 0's (that you get from 1 - .999~) actaully doesn't equal 0! Which is false.

Now why did I present it as 0x != 0? Because there are an infinite number of zero's, which I called variable 'x'. Correct me if it's not proper to present infiity as a x. What I wrote was

x * 000\infty \neq 0
When what I should have wrote was
000\infty \neq 0

By the way, is 0 \cdot \infty really undefined? news to me, I always assumed it was 0.

 

[Townsend]

By the way, is 0 \cdot \infty really undefined? news to me, I always assumed it was 0.

In calculus when evaluating limits you can get to a point like infinity times 0 and at those times it is considered indeterminate. Thus you invoke L.H...

But without knowing how you arrived at infinity times 0 I don't think anyone can really call it undefined. As far as ordinary arithmetic goes I don't see how this would be a legal operation.

Regards,

I am not an expert so please go easy if I made an error...

 

[rachmaninoff]

here we go again

if you were to perform the following operation

1 - .9 you would get .1

if you were to do
1 - .9999999999 you would get .0000000001

Now if you were to manually try to subtract .999 \infty from 1, you would get 000000000 for infintiy! hence,
1 - .999 \infty = 000 \infty Make sense? So to say that 1 - .999 \infty \neq 0 would also mean that that the infinite row of 0's (that you get from 1 - .999~) actaully doesn't equal 0! Which is false.

I see, the problem is we were misreading your (incorrect) notation. It's 0.999... or 0.\overline{9}, not .999 \infty (which looks like an attempted multiplication).

By the way, is 0 \cdot \infty really undefined? news to me, I always assumed it was 0.

Yes, arithmetic on infinity is not defined. If you attempt to define it, you get contradictory results like
\lim_{x \rightarrow 0} \frac{1}{x} \cdot x = 1
\lim_{x \rightarrow 0} \frac{1}{x} \cdot 0 = 0

This probably already occurred a dozen times in this thread, I'm too lazy to look for precedents.

Will this thread ever die?

 

[yourdadonapogostick]

Well, he is completely wrong, but \infty is well-defined (you're wrong about that), but arithmetic on \infty is not, so \infty \cdot 0 is what's undefined.

then define \infty

 

[VietDao29]

then define \infty

The greatest number of all real numbers. Obviously, you won't be able to find what number actually infinity is.
----
@eNathan:
How come 1 - 0.99... = a row of 0s? Where is the little number 1.
I agree 0.99... = 1, but your proof does not make much sense to me.
Viet Dao,

 

[bao_ho]

1 / 9 = 0.1111recuring
0.9999recuring / 9 = 0.1111recuring

then 1 = 0.9999recuring

 

[eNathan]

rachmaninoff::
Hey thanks for pointing out my error, ill use \overline{x} Instead of x infty from now on ;) Atleast you understand my point and I wasnt called a wacko :lol:

nice proof bao_ho, btw.

 

[Zurtex]

rachmaninoff::
Hey thanks for pointing out my error, ill use \overline{x} Instead of x infty from now on ;) Atleast you understand my point and I wasnt called a wacko :lol:

nice proof bao_ho, btw.

Yeah, kind of my point, with all the infinities floating round I still can't really make sense what you are saying.

 

[EnumaElish]

1 / 9 = 0.1111recuring
0.9999recuring / 9 = 0.1111recuring

then 1 = 0.9999recuring

Your 1st step assumes your conclusion, when you replace 1 with "0.9999recuring".

Sorry I forgot the latex code for <> or !=, what is it again

\ne

 

[Zurtex]

Your 1st step assumes your conclusion, when you replace 1 with "0.9999recuring".

It's not a rigorous proof on many levels but it doesn't do that. It is showing that you get the same answer when you divide both of them by 9, hence they must be the same number.

 

[EnumaElish]

Okay, I got you.

 

[gonegahgah]

It is wrong to say that 1 / 3 = 0.3...
Despite math ascertion to the otherwise it should be:
1 / 3 = 0.3... r 0.0...1
You try doing it on paper and see if you don't have to keep carrying the one.

 

[arildno]

It is wrong to say that 1 / 3 = 0.3...
Despite math ascertion to the otherwise it should be:
1 / 3 = 0.3... r 0.0...1
You try doing it on paper and see if you don't have to keep carrying the one.

Complete nonsense. Learn some maths before posting.

 

[JasonRox]

I concur with arildno.

When is the Pi=3 thread going to come back up?

 

[HallsofIvy]

The greatest number of all real numbers. Obviously, you won't be able to find what number actually infinity is.
----
@eNathan:
How come 1 - 0.99... = a row of 0s? Where is the little number 1.
I agree 0.99... = 1, but your proof does not make much sense to me.
Viet Dao,

If there WERE a "greatest number of all real numbers" many important theorems in mathematics would be untrue. Perhaps the most important of them would be the "Archimedean Property of Positive Integers": If x is any real number, there exist a positive integer, n, with n> x".

Fortunately for us all, there is NO "greatest of all real numbers" and "infinity", however you define it, is NOT a real number.

 

[Integral]

It is wrong to say that 1 / 3 = 0.3...
Despite math ascertion to the otherwise it should be:
1 / 3 = 0.3... r 0.0...1
You try doing it on paper and see if you don't have to keep carrying the one.

Fortunatly we do not have to do it on paper.

Now, I have to point out that your notation is faulty or at least it does not work the way you want it to. You seem to want to claim that .00...1 where the ellipsis represents a infinite number of zeors has meaning. In a well formed decimal number every digit must have a place value, as soon as you place the 1 you have terminated the string of zeros, thus the difference really represented is 1-.999...9 a finite length string of 9s. Of course this difference is greater then 0. Since .999... represents an endless string of 9's you can never reach the end so the 1 never appears.

Contrary to your apparent claim, infinity is NOT just a large real number.

 

[gonegahgah]

Hi Integral

The only reason we are disallowed from using 0.0...1 notation - even though it is easy to work out what is meant from the notation - is because this would destroy every proof that 1 = 0.9...
There is no other reason to disallow this notation.

But let's look at 1 / 3 seeing this is one of the simpler proofs used (although all proofs no matter how cool they look ultimately are just re-representations of this simplest proof).

Let's work it out:
1. 3 ) 1 (can't do)
2. 3 ) 1.0 = 0.3 r 0.1 (as 0.3 x 3 = 0.9)
3. 3 ) 1.00 = 0.33 r 0.01 (as 0.33 x 3 = 0.99)
4. 3 ) 1.000 = 0.333 r 0.001 (as 0.333 x 3 = 0.999)
5. 3 ) 1.0000 = 0.3333 r 0.0001 (as 0.3333 x 3 = 0.9999)
and we could attempt to keep going for ever.

And in all respects each of these answers is correct on its own.
ie 1/3 = 0.3 r 0.1 = 0.33 r 0.01 = 0.333 r 0.001 etc.

The one thing that we can clearly see from the above is that we always have a remainder. The disappointing thing is that the maintainers of the 1 = 0.9... "proof" want us to simply let that remainder drop off the edge of the universe and to just forget about it.

I know I will never be able to convince you but I do have a question that perhaps you can help me with:

Why is it so important to mathematics that 1 = 0.9...?
What is at stake?

Thanks

 

[Integral]

Hi Integral

The only reason we are disallowed from using 0.0...1 notation - even though it is easy to work out what is meant from the notation - is because this would destroy every proof that 1 = 0.9...
There is no other reason to disallow this notation.

But let's look at 1 / 3 seeing this is one of the simpler proofs used (although all proofs no matter how cool they look ultimately are just re-representations of this simplest proof).

Let's work it out:
1. 3 ) 1 (can't do)
2. 3 ) 1.0 = 0.3 r 0.1 (as 0.3 x 3 = 0.9)
3. 3 ) 1.00 = 0.33 r 0.01 (as 0.33 x 3 = 0.99)
4. 3 ) 1.000 = 0.333 r 0.001 (as 0.333 x 3 = 0.999)
5. 3 ) 1.0000 = 0.3333 r 0.0001 (as 0.3333 x 3 = 0.9999)
and we could attempt to keep going for ever.

And in all respects each of these answers is correct on its own.
ie 1/3 = 0.3 r 0.1 = 0.33 r 0.01 = 0.333 r 0.001 etc.

The one thing that we can clearly see from the above is that we always have a remainder. The disappointing thing is that the maintainers of the 1 = 0.9... "proof" want us to simply let that remainder drop off the edge of the universe and to just forget about it.

I know I will never be able to convince you but I do have a question that perhaps you can help me with:

Why is it so important to mathematics that 1 = 0.9...?
What is at stake?

Thanks

Once again infinity is NOT a very large real number. That is the way you treat it and that is why you are being fooled into thinking you are doing math.

 

[JonF]

Hi Integral

The only reason we are disallowed from using 0.0...1 notation - even though it is easy to work out what is meant from the notation - is because this would destroy every proof that 1 = 0.9...
There is no other reason to disallow this notation.

Please state a well defined definition of what "0.0...1" means and show that it is a real number. If you do this I am fairly certain everyone will let you use it in this discussion.

Why is it so important to mathematics that 1 = 0.9...?
What is at stake?

I believe completeness is at stake.

 

[gonegahgah]

Hi Integral

Is the following math correct or wrong?

1 / 3
= 0.3 r 0.1
= 0.33 r 0.01
= 0.333 r 0.001

 

[d_leet]

Hi Integral

Is the following math correct or wrong?

1 / 3
= 0.3 r 0.1
= 0.33 r 0.01
= 0.333 r 0.001

It is correct, but behavior after a finite number of steps does not dictate the behavior at infinity, certainly not in the way you are treating it.

 

[arildno]

\frac{1}{3}=0.3+\frac{1}{30}=0.33+\frac{1}{300}=0.333+\frac{1}{3000}=0.3333+\frac{1}{30000}
and so on.
Seems you didn't know what division and remainders was after all.

 

[Hurkyl]

Why is it so important to mathematics that 1 = 0.9...?

It's not. It's a rather uninteresting consequence of

(1) the axioms of the real numbers
(2) the definition of decimal representations of real numbers

 

[Diophantus]

http://en.wikipedia.org/wiki/0.999

 

[whatta]

I touched this topic before, here it goes again for you: let's solve X/10 + X/100 + X/100 + ... to some N/M. we will plug X=9 in then and see If N = M. so. above series sum is X * (1/10 + 1/100 + 1/1000 + ...)

expression in () is infinite geometric progression with a = r = 0.1, hence the sum is 0.1/(1-0.1)

which yields N = K * 0.1 * X, M = K * (1 - 0.1)

for X = 9, N = K * 0.9, M = K * 0.9

so N = M

 

[kendr_pind]

lot of unrelated chatter which doesn't really answer the real question...ie 1/9 = 0.11111... so is 1 = 0.9999999...?
Now as there are infinite numbers between 0 & 1, and suppose an insect is moving on a table...it starts at point zero and starts moving at a constant speed...so now it covers 0, 0.00000000...1, this last '1' no one knows when it comes...! now you come back after one hour and see where the insect is..definitely it would have moved,say 10cm. Now how did the insect cross infinite numbers and reach '1' cm and so on till '10' cm?