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Uthman
06-13-2008, 10:02 PM
:sl:

I hope this hasn't been posted before. I just wondered how many of you know that the decimal number 0.9999...(recurring) actually equals 1.

Allow me to prove it for you:
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:
10x - x = 9.9999... - 0.9999...
9x = 9.0000...
Divide by nine:
x = 1.0000...
Anybody want to challenge me on this? Or perhaps somebody would like to post a different proof or counter-proof? :D

:w:

truemuslim
06-13-2008, 10:06 PM
I think my math teacher told me bout this...

i remember it from LI tho....straaange...

Oooh yehH! lool i was on LI while he was talking! :X hehe

aysenil
06-13-2008, 10:08 PM
:thumbs_upwoow gr8 mashallah.... who can challenge u :D
and i dont no any other proof :?

Mikayeel
06-13-2008, 10:14 PM
:sl:

Hmm, seems interesting!, Barakalahu feek bro:D

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06-13-2008, 10:19 PM
format_quote Originally Posted by Osman
:sl:

I hope this hasn't been posted before. I just wondered how many of you know of the fact that the decimal number 0.9999...(recurring) actually equals 1.

Allow me to prove it for you:
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:
10x - x = 9.9999... - 0.9999...
9x = 9.0000...
Divide by nine:
x = 1.0000...
Anybody want to challenge me on this? Or perhaps somebody would like to post a different proof or counter-proof? :D

:w:
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:

10x - x = 9.9999... - 0.9999... <-- You subtracted x on one side, and .999 on the other so it doesn't make sense.

Since 0.3333 + 0.3333 ) 0.3333.. = 0.999..
and since 0.333.. is 1/3, then 1/3 + 1/3 + 1/3 = 1

Uthman
06-13-2008, 10:34 PM
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:

10x - x = 9.9999... - 0.9999... <-- You subtracted x on one side, and .999 on the other so it doesn't make sense.
I don't see why it doesn't make sense, since x = .999...
The same thing is still being subtracted from both sides.

Since 0.3333 + 0.3333 ) 0.3333.. = 0.999..
and since 0.333.. is 1/3, then 1/3 + 1/3 + 1/3 = 1
Good one! Of course, that's provided that 1/3 does actually equal 0.333....

Regards

06-13-2008, 10:35 PM
format_quote Originally Posted by Osman
I don't see why it doesn't make sense, since x = .999...
The same thing is still being subtracted from both sides.

Good one! Of course, that's provided that 1/3 does actually equal 0.333....

Regards
:-[ Yes I was totally wrong. 1/3 does equal 0.33333333333333 : ).

Uthman
06-13-2008, 10:38 PM
1/3 does equal 0.33333333333333 : ).
Why? Because your Maths teacher told you? :D

06-13-2008, 10:52 PM
format_quote Originally Posted by Osman
Why? Because your Maths teacher told you? :D
No, my trusty calculator :)

Uthman
06-14-2008, 09:19 AM
No, my trusty calculator :)
Oh. :-[

Sure, but aren't calculators programmed by us not-so trusty humans anyway? :?

Idris
06-14-2008, 09:53 AM
New to me.

'Abd al-Baari
06-14-2008, 09:56 AM
Assalamu Alaykum

Me too^

How about 1 - 0.999999 = 0.000001

So 1 is not equal to 0.99999 :D

WaAlaykumus Salaam Warahmatullah!

Ayoub
06-14-2008, 10:04 AM
format_quote Originally Posted by Osman
:sl:

I hope this hasn't been posted before. I just wondered how many of you know of the fact that the decimal number 0.9999...(recurring) actually equals 1.

Allow me to prove it for you:
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:
10x - x = 9.9999... - 0.9999...
9x = 9.0000...
Divide by nine:
x = 1.0000...
Anybody want to challenge me on this? Or perhaps somebody would like to post a different proof or counter-proof? :D

:w:
If x = 9, 9x does not = 9. If x = 9, 9x = 81. :)

Whatsthepoint
06-14-2008, 10:42 AM
format_quote Originally Posted by Ayoub
If x = 9, 9x does not = 9. If x = 9, 9x = 81. :)
Wha..?
:-[

Abdul Fattah
06-14-2008, 10:47 AM
The problem is the surrealism of infinity. In the real world where infinity doesn't exist, then in step 3 where you subtract x, there you'll see that the 9.999... always has one decimal less behind the point than 0.9999...
That way the subtractions can never become 9. So the calculations themself are fine, it's the mathematical axiom of infinity that is dodgy.

The same happens for 1/3 = 0.333... that only works with an infinite number of factors. In reality it's impossible to calculate with that, so we calculate in approximations (so does your calculator).

Uthman
06-14-2008, 10:57 AM
:sl:

format_quote Originally Posted by Abdul Baari
How about 1 - 0.999999 = 0.000001

So 1 is not equal to 0.99999 :D
:D

Yes, but remember that the 0.999... is a recurring decimal with an infinite number of nines. For this reason, 1 - 0.9999.... would result in 0.0000000......

There would be an infinite number of zero's in the answer so there would be no 1 at the end because there is no end!

:w:

Uthman
06-14-2008, 10:59 AM
:sl:

format_quote Originally Posted by Ayoub
If x = 9, 9x does not = 9. If x = 9, 9x = 81. :)
That certainly makes sense, but the argument here is that 0.9999... = 1, where x = 0.99999...

Nobody claimed that x = 9! :)

:w:

Abdul Fattah
06-14-2008, 11:54 AM
To clarify the previous post, consider the same calculation, only this time with finite numbers instead of infinite numbers:

x = 0.9999
Multiply both sides by ten:
10x = 9.999
Subtract x from both sides:
10x - x = 9.999 - 0.9999
9x = 8.9991
Divide by nine:
x = 0.9999

06-14-2008, 12:20 PM
:sl:

Subtract x from both sides:
10x - x = 9.9999... - 0.9999...
9x = 9.0000...
How come 10x - x becomes 9x, when x=0.9999...? :exhausted

tetsujin
06-14-2008, 01:19 PM
format_quote Originally Posted by Osman
:sl:

I hope this hasn't been posted before. I just wondered how many of you know of the fact that the decimal number 0.9999...(recurring) actually equals 1.

Allow me to prove it for you:
Let
x = 0.9999...
Multiply both sides by ten:
10x = 9.9999...
Subtract x from both sides:
10x - x = 9.9999... - 0.9999...
9x = 9.0000...
Divide by nine:
x = 1.0000...
Anybody want to challenge me on this? Or perhaps somebody would like to post a different proof or counter-proof? :D

:w:
Who ever showed you that needs to get a good smack in the head.

I suggest you go to a good math teacher and allow them to properly educate you on the rules of mathematics.

Your "equation" boils down to ((x * 10) - x)/9 = something

You've allowed x to be an irrational number, which is fine, but that's where you are having difficulties. Logically speaking, ((x * 10) - x)/9 should equal x again.

Try .888888888 and see what you get with your logic.

(0.888888888..... * 10 - 0.888888888..... )/8 = ?
(8.888888888..... - 0.888888888..... )/8 = What do you think it should be?

Please don't make a mockery of mathematics.

All the best wishes,

Faysal

crayon
06-14-2008, 01:40 PM
format_quote Originally Posted by tetsujin
Please don't make a mockery of mathematics.

Please don't be such a jerk.

All the best wishes,

Faysal
...

Uthman
06-14-2008, 01:49 PM
x=0.8888....
10x = 8.888888
9x = 8
x = 8/9 = 0.8888...

:)

Logically speaking, ((x * 10) - x)/9 should equal x again.
And it does. In the proof that I showed, x = 0.9999... and x = 1. The argument is that both are therefore the same.

Please don't make a mockery of mathematics.
I assure you that I am doing nothing of the sort. Mathematics is based upon proof, not intuition. What I posted was one such proof, there are many others. If you disagree, then please argue with a counter-proof. This particular case is believed by many professional mathematicians themselves, who I would assume know more than you and I about the 'rules of Mathematics'.

Finally, I would request that we please stay respectful. This is posted in the 'puzzles and humour' section and it isn't to be taken too seriously. :)

Regards

tetsujin
06-14-2008, 01:52 PM
format_quote Originally Posted by Osman
Finally, I would request that we please stay respectful. This is posted in the 'puzzles and humour' section and it isn't to be taken too seriously. :)

Regards

I apologize, I love math too much for my own good.

All the best wishes,

Faysal

Uthman
06-14-2008, 01:54 PM
Haha, no worries. I love maths too. :)

:-[

Abdul Fattah
06-14-2008, 04:22 PM
Hi Tetsujin
format_quote Originally Posted by tetsujin
Please don't make a mockery of mathematics.

All the best wishes,

Faysal
I don't think this is making a mockery out of it. Some advanced math classes even study these false proofs. If anything, they help people have a better understanding of math, or in this case a better understanding of the problems with working with infinity.

Edit: I see I was to late with my reply, just ignore then ^_^

Uthman
06-15-2008, 04:46 PM

He asked me to calculate 0.99999.... + 0.11111....

I worked it out and the answer comes to 1.11111....

That is the same as 1 + 0.1111....

With me? :D Anybody got a problem with that?

'Abd al-Baari
06-15-2008, 04:50 PM
:sl:

He asked me to calculate 0.99999.... + 0.11111....

I worked it out and the answer comes to 1.11111....

That is the same as 1 + 0.1111....
Wow i just tried that, and it worked..You learn something new everyday..:p

JazakAllah Khayr akhee. :)

:w:

Abdul Fattah
06-15-2008, 04:57 PM
Again the same problem as before.
With a finite number of factors we would get:
0.99999 + 0.11111 = 1.11110
1.11110 = 1 + 0.11110
The problem lies with this axiom:
∞+1=∞

So that means that 1.1111... - 0.0000...1 = 1.1111...
The numbers are only equal because the difference is ignored next to infinity. Remember: infinity is not a number, its' a concept.

Uthman
06-15-2008, 05:06 PM
I agree with you that inifinity is what poses the problem here. But Akhee, you are speaking of infinity as though it is a number when it isn't. It is a concept, not a quantity!

EDIT: Ok, never mind.

Abdul Fattah
06-15-2008, 05:30 PM
format_quote Originally Posted by Osman
I agree with you that inifinity is what poses the problem here. But Akhee, you are speaking of infinity as though it is a number when it isn't. It is a concept, not a quantity!

EDIT: Ok, never mind.
It seems I edited my post just a few minutes before you were able to make yours :p
Anyway, on another note, irrational numbers really are irrational in the sense that they aren't necessarily real quantities either! In math we can have infinite terms in an irrational number. Like we can divide the number 1 by the the number two an infinite number of times.
1/2=0.5
0.5/2=0.25
0.25/2=0.125
...
But is that realistic? Say we have a lump of clay, can we divide that into two smaller lumps an infinite number of times? eventually you'll be dividing molecules, atoms, quarks, strings? Is there any guarantee you can repeat this division infinitely? So you could say numbers which are infinitely small or have infinitely small parts (like 1.11111... ) are also concepts rather then quantities just as we both pointed out is the case with infinity itself. This again shows the problem with these proofs, the calculations used treat the irrational numbers like rational numbers.

Uthman
06-15-2008, 05:37 PM
format_quote Originally Posted by Abdul Fattah
the calculations used treat the irrational numbers like rational numbers.
Very good point! I agree with your post. :) Also on a more general level, more often than not, theory differs from reality anyway.

I love to tease people with this. It's so funny seeing my brother know full well that 0.999... and 1 are different numbers but not being able to prove it. :D

I get a sick sense of pleasure out of it. Maybe I need to get my head checked. +o(

Uthman
06-18-2008, 12:04 PM