0.999 =1 is LUB or exactly the same

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Discussion Overview

The discussion centers around the mathematical relationship between the repeating decimal 0.999... and the number 1. Participants explore whether 0.999... is merely the least upper bound (supremum) of a set of numbers approaching 1 or if they are exactly the same value. The conversation includes aspects of mathematical reasoning and conceptual clarification.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants assert that 0.999... is equal to 1, particularly when considering the infinite nature of the decimal representation.
  • Others clarify that while 1 is the supremum of the set {0.9, 0.99, 0.999, ...}, this does not negate the assertion that 0.999... equals 1.
  • A participant emphasizes that the terms least upper bound (l.u.b.) and greatest lower bound (g.l.b.) apply to sets rather than individual numbers, providing examples to illustrate this point.
  • One participant presents a mathematical argument using the fraction 1/3 and its decimal representation to demonstrate that 0.999... equals 1.
  • Another participant expresses surprise at the ongoing discussion, reiterating that 0.999... is exactly equal to 1 and linking this to the concept of supremum.

Areas of Agreement / Disagreement

Participants generally agree that 0.999... equals 1, but there is some contention regarding the interpretation of supremum and its implications for understanding this equality. The discussion remains somewhat unresolved as participants explore different perspectives.

Contextual Notes

Some statements rely on the understanding of infinite decimal representations and the definitions of supremum and infimum, which may not be universally accepted or understood in the same way by all participants.

Algorithm
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I want to ask that we say 0.999...=1 because the 1 is the least upper bound (supremum) of 0.999... or are they exactly same numbers.

I ask this because i am confused with finding (the infimum) the largest lower bound of 1. Do you think it should be 0.999... or is 0.999...=1.

Thanks for your comments...
 
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If you have a set [itex]S = \left\{ {0.9,0.99,0.999,0.9999,...} \right\}[/itex] then 1 is indeed the supremum. But [itex]0.999... = 1[/itex], at least if you mean a 0 with an infinite number of decimal 9's.

You may want to read this topic.
 
Algorithm said:
I want to ask that we say 0.999...=1 because the 1 is the least upper bound (supremum) of 0.999... or are they exactly same numbers.

I ask this because i am confused with finding (the infimum) the largest lower bound of 1. Do you think it should be 0.999... or is 0.999...=1.

Thanks for your comments...
The terms l.u.b. or g.l.b. are for sets, not individual numbers.

E.g., the l.u.b. of [0,1) is 1. The g.l.b. of [0,1) is 0.

The l.u.b. and g.l.b. of {1} is 1.
 
1/3= 0.333...

Can be expressed by the serie

3/10 + 3/100 + 3/1000...

1/3 * 3 = 1

so

3*(3/10 + 3/100 + 3/1000...)

9/10 + 9/100 + 9/1000...

That is 0.999...

so 0.999... = 1
 
I can't believe this is here! I just responded to a new post in the "archives" about this same topic! 0.9999... is exactly equal to 1! Yes, 1 is also the supremum of the set {0.9, 0.99, 0.999, ...} but that is exactly the same as saying 0.999... = 1!
 

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