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# 0 or 1 ??

what is the value of $$[0.9999999999999999...]$$ ??

here $$[x]$$ represents the greatest integer function.

Note by Rohit Kumar
1 year, 12 months ago

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The thing that most people have confusion about is the infinite number of $$9$$s after the decimal.They tend to think that $$.999999...$$ approaches $$1$$ but never quite reaches $$1$$. First thing to realize is that $$.999...$$ does not only reach one but it is exactly equal to $$1$$,and when I say exactly,I really mean it.Now,computing the above expression is a simple matter of substituting $$1$$ in place of $$.99999...$$.

If you still aren't contented,then think about it this way.What do we mean when we say that two real numbers are different?It means that there is at least one more real number between them(In fact there are an infinite number of them). Now answer this:Can you find any other real number between $$1$$ and $$.9999....$$?If you can't ,the only conclusion is that they are equal. · 1 year, 12 months ago

1 · 1 year, 12 months ago

The Value = 1

let X = 0.999999999999999999 ......

then 10 X = 9.999999999999999 ......

subtract (10 X - X) = 9 X = 9 =====> X =1 · 1 year, 12 months ago

yes the answer is one. one of example why 0,9999..........=1. look 10/3= 3,33333333333333..... then 10= 3times3.333333333....................... 10=9.9999999999999999. next 10= 9+0.99999999..............................subtract 10-9=0.9999999......... so 1=0.999999999999........ · 1 year, 12 months ago

The value of the expression will be zero and not one. Since the value of $$X$$ which is given approaches the value of one but it really does not become equal to it and will always remain less than it and thus $$[X] = 0$$. · 1 year, 12 months ago

The value is $$1$$.

This is basically asking the greatest integer that is less than or equal to the limit of $$1-{10}^{-n}$$ as $$n$$ approaches infinity. Since the limit is $$1$$, so is the final answer. The order matters. · 1 year, 12 months ago

Comment deleted Feb 07, 2015

You have computed the floor of values that only have a finite number of $$9$$'s after the decimal.A brilliant way to think about this is :Can you find any other number between $$1$$ and $$.9999....$$?If you can't the only conclusion is that they are equal. · 1 year, 12 months ago

Wolframalpha does not disagree:

http://m.wolframalpha.com/input/?i=floor+0.999...&x=0&y=0

The problem is that you have computed a finite number of 9's, as stated by @Rahul Saha . The floor function of 0.99999 is 0, but the floor of 0.9... (with an infinite number of 9's) is 1. That's because this number is equal to 1, as proved in many different ways by @Ossama Ismail , @Mursalin Habib and Rahul Saha · 1 year, 11 months ago

Comment deleted Feb 07, 2015

So what is the conclusion 1 or 0. · 1 year, 12 months ago

AS THIS IS AN INFINITE SUM I.E 0+9/10+9/100...................... SO ON AND SO FOURTH, WE SEE THAT ITS VALUE APPROCHES 1. WELL I DONT UNDERSTAND THE STIGMA/CONUNDRUM HERE. THIS FITS RATHER PERFECTLY INTO THE DEFINITION OF GIF THAT GIF OF ALL NUMBERS LYING BETWEEN 2 INTEGERS IS EQUAL TO THE INTEGER LESS THAN OR EQUAL TO IT. HERE 0.9999999999999999999999........... CAN BE TREATED AS THE LAST REAL NUMBER B/W 0 AND 1 AS IT NEVER REACHES ZERO. SOME WILL ARGUE THAT TO MAINTAIN CONTINUITY WE WILL REGARD IT AS ONE BUT THINK AGAIN.

INFINITE IS NOT DEFINED OR RESTRICTED HENCE IT CAN BE DIFFERENT FOR YOU AND ME BUT WIL STILL BE THE SAME.

AND AS FAR AS CONTINUITY IS CONCERNED IF YOU HAVE A LINE MADE UP OF INFINTELY SMALL POINTS , REMOVING SOME WILL NOT MAKE IT DSICONTINOUS. HENCE IT IS ZERO. · 1 year, 7 months ago

I don't know much about continuity but I think an infinite geometric series as defined as the limit of the geometric series as it approaches infinity. Thus $$.999\cdots =1$$ follows by applying the definition.

Btw, what do you mean by the last real number between two numbers.? If there aren't an infinite number of real numbers between $$a$$ and $$b$$, then $$a=b$$. A "last real number" can't exist in an open interval like $$(0,1)$$. · 1 year, 7 months ago

Is 0.9999999999999999999.... an integer? · 1 year, 10 months ago

Yes, it is. · 1 year, 10 months ago

What I think is that the main question here is that whether 0.9999999...... is equal to 1 or not.and that I think it is.Therefore the answer should be 1. · 1 year, 12 months ago

agreed. · 1 year, 11 months ago

AS THIS IS AN INFINITE SUM I.E 0+9/10+9/100...................... SO ON AND SO FOURTH, WE SEE THAT ITS VALUE APPROCHES 1. WELL I DONT UNDERSTAND THE STIGMA/CONUNDRUM HERE. THIS FITS RATHER PERFECTLY INTO THE DEFINITION OF GIF THAT GIF OF ALL NUMBERS LYING BETWEEN 2 INTEGERS IS EQUAL TO THE INTEGER LESS THAN OR EQUAL TO IT. HERE 0.9999999999999999999999........... CAN BE TREATED AS THE LAST REAL NUMBER B/W 0 AND 1 AS IT NEVER REACHES ZERO. SOME WILL ARGUE THAT TO MAINTAIN CONTINUITY WE WILL REGARD IT AS ONE BUT THINK AGAIN.

INFINITE IS NOT DEFINED OR RESTRICTED HENCE IT CAN BE DIFFERENT FOR YOU AND ME BUT WIL STILL BE THE SAME.

AND AS FAR AS CONTINUITY IS CONCERNED IF YOU HAVE A LINE MADE UP OF INFINTELY SMALL POINTS , REMOVING SOME WILL NOT MAKE IT DSICONTINOUS. HENCE IT IS ZERO. · 1 year, 7 months ago