Felix~

You are correct that the sequence of numbers

0.9
0.99
0.999
...

asymptotically approaches 1; however, the number 0.9999... (with an infinite
number of 9s) is equal to 1.  The formal proof of this is fairly tricky as
the definition of the real number is usually done as an equivalence class of
Cauchy sequences; a simplified version of the proof can be thought of as
follows:

For any two real numbers *a* and *b* there exists an infinite number of real
numbers *c *such that *a < c < b*.  However, there do not exist any numbers
between 0.99999... and 1, thus they must be same number.

As it turns out, it took mathematicians a long time to nail down formally
exactly what we naively think of as "numbers".

Matt

On Wed, Oct 13, 2010 at 6:27 PM, Felix H. Dahlke <f...@ubercode.de> wrote:

> On 13/10/10 22:28, David Sletten wrote:
> >
> > On Oct 12, 2010, at 5:44 PM, Brian Hurt wrote:
> >
> >>   For example, in base 10, 1/3 * 3 = 0.99999...
> >
> > It may seem counterintuitive, but that statement is perfectly true.
> > 1 = 0.9999...
> >
> > That's a good test of how well you understand infinity.
>
> I'm clearly not a mathematician, but doesn't 0.99999... asymptotically
> approach 1, i.e. never reaching it? How is that the same as 1?
>
>

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