Holy fsck people.
0.999... DOESN'T APPROACH ANYTHING. IT'S NOT GETTING LARGER.
It just IS 1.
You are still thinking about writing a zero, then adding a decimal point, and then adding a nine, then another, then another...
If you do that, then no, what you write down will never equal 1 because it's a progression. We are NOT talking about that though. We are talking about an already infinite string of 9s. Not a string to which you add nines without end. There is a HUGE difference.
Do the freaking subtraction.
1.0000000000000000000000 -
0.9999999999999999999999
---------------------------------------
0.0000000000000000000000
as you can clearly see, their difference is a 0, followed by a decimal point, followed by an infinite string of 0s. Or, as most normal folk like to call it, just plain ol' 0.
You can also do it by long division. I don't think anyone here will disagree with me when I say that 1/1 = 1 right? What if I could prove via long division that 1/1 = 0.999...?
You must be able to accept one thing though. We can say that 3 goes into 6 twice with a remainder of 0, or we can say that 3 goes into 6 once with a remainder of 3, or 0 times with a remainder of 6. All statements are equivalent. Keeping that in mind:
_____________________________________
1)1.000000000000000000000000000000000... <--- supposed to be 1 into 1.000...
Now, we can do it the easy way and say 1 goes into 1 once, remainder 0 and be done with it, or we can do the following:
1 goes into 1 0 times, remainder 1. We are left with:
_0.___________________________________
1)1.000000000000000000000000000000000...
__0
Now, let's do the subtraction.
_0.___________________________________
1)1.000000000000000000000000000000000...
__0
__10
Okay. Now let's say that 1 goes into 10 9 times, remainder 1.
_0.9___________________________________
1)1.000000000000000000000000000000000...
__0
__10
___9
Subtract.
_0.9___________________________________
1)1.000000000000000000000000000000000...
__0
__10
___9
___1
Bring down the 0
_0.9___________________________________
1)1.000000000000000000000000000000000...
__0
__10
___9
___10
1 goes into 10 9 times, remainder 1.
0.99___________________________________
1)1.000000000000000000000000000000000...
__0
__10
___9
___10
____9
repeat ad infinitum
I think the point is pretty obvious here.