we let x = 0.9(bar)
then 10x = 9.9(bar) since the 9s goes on for ever
10x-9 = 0.9(bar)
10x-9 = x (see above)
9x = 9
x = 9/9
x = 1
0.9(bar) = 1
.. and there you have it!
/Jonas Hartwig
yl...@dataphone.se
>I've seen that some of you have difficulties in understanding
>the fact that 0.9(bar) infact is the same number as 1. Here
>comes a proof:
>we let x = 0.9(bar)
>then 10x = 9.9(bar) since the 9s goes on for ever
Nope.
10x < 9.9(bar)
0.9(bar) ^ infinity = 0.0(bar)
1 ^ infinity = 1
therefore 0.9(bar) is not equal to 1.
--
* Dan Markham * Peanut butter on a *
* bla...@wwa.com * sand tire gets frozen *
* Game Programmer * on the rusty star of *
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--
Stan Armstrong
Prove it.
|>0.9(bar) ^ infinity = 0.0(bar)
Prove it.
|>1 ^ infinity = 1
One out of three correct so far.
|>therefore 0.9(bar) is not equal to 1.
You can't prove something if your assumptions are wrong.
--
J Lee Jaap <Jaa...@ASMSun.LaRC.NASA.Gov> +1 757/865-7093
employed by, not necessarily speaking for,
AS&M Inc, Hampton VA 23666-1340
What if you were to define .(9bar) recursively, thereby avoiding the entire
issue of infinity, infinite sums, etc.?
This is what I mean: Let's define a new symbol, a, which will function just
like a digit but isn't an already defined thing. For instance,
.a means a/10,
.0a means a/100,
.9a means .9 + a/100
...and so on.
In particular, we'd like it to have the property that .a = .9a, because it
would then follow that .a = .9a = .99a = .999a = ...
So let's suppose such a thing exists. Then we'd have:
.a = .9a Multiply by 100;
10 * a = 90 + a
9 * a = 90
a = 10 (1)
It can be verified that if a = 10, then in fact .a = .9a = .99a = ...
and so such a thing is well-defined.
Let b = 9.(9bar). Observe that .b = .(9bar) = .9(9bar) = .9b, and so by
the argument above, b = 10.
Equivalently, .(9bar) = 1 .
This proof does not use infinity, so there shouldn't be any objections to it
on that ground. I suppose I could have spent more time giving a really really
solid exposition, in which all the notation was carefully laid out, but that
would reduce to the same core argument. Modulo that, I believe this is a
proof, independent of any underlying notions of limiting values or whatever.
Yours,
Brad Ballinger
Out-To-Luncher Extraordinaire
r^infinity = 0 if and only if abs(r) < 1. Thus stating .9(bar)^infinity
= 0 assumes .9(bar) does not equal 1. You can't prove a fact by assuming
its true!
Robin
And oh my god .... we are back to square one :)