Monday, 8 July 2013

infinity - If 0.999cdots=1 Then Does frac110infty=0?




Recently I stumbled across a, to me, rather strange idea. I was messing around with the proof of 0.999...=1, when I figured that what 0.999... means is that those are all nines. That way I came upon a weird idea. Say a=0.999..., then a=1x. Yet, how do we define what x is? It should say x=0, but my theory did not. If 0.999... is just an endless sequence of nines, then why can't we say x just is an endless sequence of zeroes, ending with a 1, like 110?
If we take the equation n=0.9

for example, then, what would 1n be? Yes indeed, 0.1. Following that theory, can't we say that 0.999...=1110
Now, if 0.999...=1 this would be impossible. Go figure. 1=1110
then 110=0
but that is impossible, because we cannot say 100=1
When I came to this point, I really got stuck, because, in my head everything I did was right, however, it is impossible. Can somebody please explain to me what mistakes I may have made, and enlighten me about what else I did wrong?




Thanks in advance.
Sjoerd Dorrestijn.



EDT: I prefer 110 to use as an indication of 0.000...01, even though 10= in some way, I just seem to find this more clear.



EDT2: Just to be clear, I read a proof that 0.999...9=1 because it'd be 10.000...0=10=1. What I tried to prove here is that it is not equal to 1, because otherwise maths would collapse. My question was whether I am right or wrong. Since the original statement uses infinity (an infinite amount of nines) I think it is a must to use infinity as well. So, the question is if either the original statement is false, or if I made a mistake somewhere.


Answer



The (proven true) statement that 0.999=1 means that limn0.9999n=1. That in turn is equivalent to limn(10.9999n)=0. Now note that 10.9999n=110n, so we have limn110n=0.




However, although the above reasoning works, it is easier and more straightforward to conclude that limn110n=0 directly from the definition of the limit, without ever considering 0.999.



Finally, it is advisable to avoid the notation 110 altogether, as it is not defined given the usual definition of its constituent symbols.


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