.999 = 1?

I’m sorry, but you don’t understand the concept of infinity. At all. You don’t understand how it works in analysis or set theory. You never “arrive” at infinity. There isn’t an “infinity-th” digit on 0.999…, there isn’t a number “infinity” on the real number line, and at any point where a function might colloquially be valued at infinity, it is considered “not defined”. There is almost no point in mathematics where is it considered valid to insert “infinity” into your equation - the only point where it is more than colloquially valid is as the x_0 for a limes, or as a value for a limes. Strictly speaking, while we all can generally grasp what c is in 10^-infinity = c (it’s zero), this usage makes mathematicians cry. It’s simply not valid. Infinity, as a concept, is something you approach. It’s not a number.

It’s very simple - “limes of x -> x_0 = infinity” is a meaningful mathematical statement; “x = infinity” is not. That’s how we distinguish between them. :rolleyes:

Ah, another value that doesn’t actually exist. Please, either prove that the infinitesimal exists and define it, or shut up about it. This is something you basically invented out of whole cloth, and have still neither defined nor provided any explanation of how it is not equal to zero. In fact, using set theory, it has been proven to you several times that according to your definitions, Z is not a real number, Z+1=inf makes no sense whatsoever, and your infinitesimal is zero. You have offered neither rebuttal nor anything to back up your unsupported and unsupportable claims in the first place.

Do you even understand the concept of limes? Like, at all? Dude, seriously. Why don’t you do yourself a favor and stop talking about mathematics when you obviously have no clue about it? You can’t even perform a long division of
1/3!

No, you showed how you think infinity is usually thought to be accessed. And you were wrong. Almost fractally wrong, come to think of it.

So is Z not a real number, or is infinity a real number?

The answer to that calculation is infinity. But only because of the limes.

…What

This is a word salad of non-sequiturs and missed points. No, we do not need to find a place for infinity. It’s not on the number line. That the number line tends towards infinity simply means that it goes on forever, and that you can get as large as you want. It is never equal to infinity - infinity is not on the line. But regardless of how meaningless this proof is, the fact of the matter remains that If Z element of R, Y element of R, X not element of R, then Z+Y = X IS FALSE.

If 0.999… means nines to infinity, then infinity must exist. It is not a quantity, rather a quality.

What is 1 - 0.999… equal to, other than 0.000… ?

Is the differential a real number? No, it’s not. I’m surprised no one yells at me for using these as discreet numbers, because apparently, they’re not that either.

Small correction to the phrasing used above: For “the limit as x approaches 1 for the function f(x) = x is 1” … we can say “As x gets closer and closer to 1, then f(x) gets closer and closer to 1” … it’s ye ol’ delta/epsilon proof.

Hey, 7777777, what is the flaw in this proof?

  1. x = 0.333…
  2. 10x = 3.333…
  3. 3 + x = 3.333…
  4. 10x = 3 + x
  5. 9x = 3
  6. x = 3/9
  7. x = 1/3
  8. 0.333… = 1/3

It seems to me that you’re avoiding answering my question. It seems to me that you CAN’T find a flaw in this proof. So you’re pretending that my question doesn’t exist.

Because if there’s no flaw in this proof, then 1/3 = 0.333…

And if 1/3 = 0.333… , then 1 = 0.999…

This is defined and true in every case. Ye ol’ closure axiom.

Read again. That’s what I’m working from. :wink: X is not element of R.

Read? I’m just cherry-picking looking for chances to use long words that’ll make me sound as smart as Indistinguishable. [giggle] … but point taken, thank you, may I have another?

Sure - you understand the issue infinitely better than some other person here.

Infinity never really shows up in high school Algebra … a/0 is given as undefined. It’s not until we start grappling with first order derivatives that we have to deal with it.

This is among the best answers I got here. If 1/3 = 0.3333…,then
1=0.9999…

Apparently, if 1/3 ≠ 0.3333…, then 1 ≠ 0.9999…

Let’s see what you have done. I have written your proof upside down to better
see what you have done.

  1. 0.333… = 1/3
  2. x = 1/3
  3. x = 3/9
  4. 9x = 3
  5. 10x = 3 + x
  6. 3 + x = 3.333…
  7. 10x = 3.333…
  8. x = 0.333…

It seems that you have just written that
x=0.333…step 1)
x=1/3 steps 6) and 7)

Do you think, what you have written differs from writing directly that
1/3 = 0.333…?
You said that if there is no flaw in your proof, then then 1/3= 0.333…
Apparently, if there is a flaw then 1/3 ≠ 0.3333…
The flaw is that you did not prove anything, you just wrote that
x=1/3
x=0.333…
1/3 = 0.333…
How about this “proof”:

1/3 = 1/3
0.333…= 0.333…

1/3=0.333…

What is the flaw in this “proof”?

OMG. I think you just broke the Internet.

What makes you think that reordering a proof as you did is a fair thing?

All men are mortal AND Socrates was a man
THEREFORE
Socrates was a mortal

is a perfectly fine syllogism

Whereas
Socrates was mortal
THEREFORE
All men are mortal AND Socrates was a man

plainly isn’t

The answer is you can’t unless all implications in the proof are of the form if and only if.
Steps 1) and 2) are like that:
x = 0.333… IMPLIES that 10x = 3.333…
but also
10x = 3.333… IMPLIES that x = 0.333…

Where is the flaw in your proof? The conclusion does not follow from the premises. Do you need another?

In all seriousness, you don’t seem to be able to follow proofs. Perhaps you are not just not experienced enough to insert the implicit commentary that most people take for granted.

You can’t invert the order - you seem to think you can, but you don’t realise that not all of the steps are reversible.

So lets spell it out fully what the commentary you are missing is.

  1. Let x = 0.33333…
  2. Apply standard rules of multiplication to the terms of (1) - Thus 10 * x = 3.3333…
  3. Apply standard algebraic manipulation to - add 3 to each side of (1) Thus 3 + x = 3.3333…
  4. Taking result from (3) and (4) we see they are the same. Thus 10x = 3 + x
  5. Taking the result from (4) subtract x from each side. Thus 9x = 3
  6. Taking the result from (5) divide both side by 9. Thus x = 3/9
  7. Simplifying 3/9 from (6) we get x = 1/3
  8. Taking our initial value of x from (1) and substituting for x in (7) we get 1/3 = 0.33333…
    QED.

It make exactly no sense to reverse the order.

I did not reorder a proof.

If you look at it, the numbers of the steps of the proof are still the same.
You can proceed from step 1) to 8) as before. I have changed nothing.

It seems that you are deliberately misinterpreting what I say. Every single word that
I say you twist to suit your purposes.

Do you think what you are doing constitutes a fair thing?

Typo - should read :
4. Taking results from (2) and (3) we see they are the same. Thus 10x = 3 + x

Just broke 100,000 reads on the thread as well. Clearly time to party - or something.

More like weep, I think. Fourteen years and counting…

No, he laid out a step by step argument that proves that 1/3 = 0.33333… Follow along steps 2 through 6 and you arrive at the conclusion that the two representations must be equal.

It appears that you are either ignoring the meat of the proof because you dislike the conclusion or you don’t understand how proofs work. Francis Vaughan supplied the annotated version to remove any possible misinterpretation, does that help you understand how the proof works? Do you have objections to any of the steps outlined in that post? Take them one by one and raise your hand when you find a problem.

It started you!

Funny that’s!

Hilarious! Yes, if you write the steps of a proof backwards it will certainly appear as though the conclusions are merely being asserted instead of proved!

Let’s try again, shall we? Proceeding in order, from step 1 to step 8, where is the error in this proof?

  1. x = 0.333…
  2. 10x = 3.333…
  3. 3 + x = 3.333…
  4. 10x = 3 + x
  5. 9x = 3
  6. x = 3/9
  7. x = 1/3
  8. 0.333… = 1/3

For example, you might say that:

10 * 0.333… does not equal 3.333…

Or you might say that:

3 + 0.333… does not equal 3.333…

Or you might claim that the error lies somewhere else. At which step, precisely, does the error lie?