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does .9 repeating equal one?

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  • #16
    Originally posted by Asher
    Absolutely not.
    Absolutely yes, and I think we may starting a break-through on Asher's problem.
    Life is not measured by the number of breaths you take, but by the moments that take your breath away.
    "Hating America is something best left to Mobius. He is an expert Yank hater.
    He also hates Texans and Australians, he does diversify." ~ Braindead

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    • #17
      Originally posted by SlowwHand
      Absolutely yes, and I think we may starting a break-through on Asher's problem.

      ESL?
      "The issue is there are still many people out there that use religion as a crutch for bigotry and hate. Like Ben."
      Ben Kenobi: "That means I'm doing something right. "

      Comment


      • #18
        Frogger:
        when I talk about the decimal representation I am talking about an element which has this form:
        xxxxxxxx.xxxxxxx...........
        where x is a digit between 0 and 9 and which could extend to the infinite, I am not talking about rational numbers (which are not biyective to the real numbers).

        This decimal representation number system has the same cardinal than the real numbers, there is a mapping between them that is both injective and suryective.

        The inyection is easy, it is clearly seen that the real numbers are included in this set.
        The surjection is somewhat trickier. It is possible to show that this set includes both this sets:
        - the set of numbers which do not end with a repeating 9 (which are easily shown to be bijective to the real numbers)
        - the set of numbers which do end with a repeating 9 (which are numerable).

        Since c (the cardinal of R) + Aleph_O (the cardinal of a numberable set) equals c, then they are both coordinable between themselves.

        A complete set is a set which, in an informal way, does not have successions which converge to "ghost" (i.e., inexistent) points. More formally, every Cauchy sequence does have a limit.
        I have said in a post before this that the set of decimal representable numbers are not complete, which is not right. First is necesary to define a distance between points to talk about completeness.

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        • #19
          Originally posted by Asher
          The reason why there's disagreement is because math is such a stupid field.

          Like it seems the most common approach these days is to use the logic that something like 1/3 is 0.3 repeating, so 3/3 must be 0.9 repeating, but it's also 1, therefore they're equal...
          Asher, have you ever learnt what a limit is?

          Take the limit of the sequence 0.9, 0.99, 0.999, ...

          By inspection 0.9999999.... is a limit

          By going over the definition of the requirements of being a limit, 1 is also a limit.

          By a fairly standard proof, if a sequence has a and b as limits, then a=b
          12-17-10 Mohamed Bouazizi NEVER FORGET
          Stadtluft Macht Frei
          Killing it is the new killing it
          Ultima Ratio Regum

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          • #20
            Originally posted by Frogger
            Asher, have you ever learnt what a limit is?

            Take the limit of the sequence 0.9, 0.99, 0.999, ...

            By inspection 0.9999999.... is a limit

            By going over the definition of the requirements of being a limit, 1 is also a limit.

            By a fairly standard proof, if a sequence has a and b as limits, then a=b
            Yes yes, I know that you can formally prove it now.
            And yes, I've taken Calculus I and II and courses with combinatorial proofs.

            I just don't like assuming repeating numbers are anything else other than repeating numbers. It would have helped if I read his post other than just the title, but it's still a silly math rule to get around how math geeks still haven't come up with a better representation of numbers.
            "The issue is there are still many people out there that use religion as a crutch for bigotry and hate. Like Ben."
            Ben Kenobi: "That means I'm doing something right. "

            Comment


            • #21
              Originally posted by alofatti
              Frogger:
              when I talk about the decimal representation I am talking about an element which has this form:
              xxxxxxxx.xxxxxxx...........
              where x is a digit between 0 and 9 and which could extend to the infinite, I am not talking about rational numbers (which are not biyective to the real numbers).

              This decimal representation number system has the same cardinal than the real numbers, there is a mapping between them that is both injective and suryective.

              The inyection is easy, it is clearly seen that the real numbers are included in this set.
              The surjection is somewhat trickier. It is possible to show that this set includes both this sets:
              - the set of numbers which do not end with a repeating 9 (which are easily shown to be bijective to the real numbers)
              - the set of numbers which do end with a repeating 9 (which are numerable).

              Since c (the cardinal of R) + Aleph_O (the cardinal of a numberable set) equals c, then they are both coordinable between themselves.

              A complete set is a set which, in an informal way, does not have successions which converge to "ghost" (i.e., inexistent) points. More formally, every Cauchy sequence does have a limit.
              I have said in a post before this that the set of decimal representable numbers are not complete, which is not right. First is necesary to define a distance between points to talk about completeness.
              You're absolutely and fundamentally wrong here.

              Under the standard decimal representation of the real numbers, every real number has a decimal representation (i.e. Decimal->Real is onto). Unfortunately, the representation is not a bijection, as 0.999999999.... and 1 are both mapped to the same real number.

              BTW, when you use the word "complete", most people use the word "closed" to represent a set which contains all of its limit points. And the set of reals and the set of decimal reps are both closed.
              12-17-10 Mohamed Bouazizi NEVER FORGET
              Stadtluft Macht Frei
              Killing it is the new killing it
              Ultima Ratio Regum

              Comment


              • #22
                You are not obliged to have o.9999..... equal to 1.
                You could very well define your own number system where 0.9999... is not 1 (as well it is correctly defined), though perhaps it would share very little resemblance to the real system.

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                • #23
                  Originally posted by Asher

                  Yes yes, I know that you can formally prove it now.
                  And yes, I've taken Calculus I and II and courses with combinatorial proofs.

                  I just don't like assuming repeating numbers are anything else other than repeating numbers. It would have helped if I read his post other than just the title, but it's still a silly math rule to get around how math geeks still haven't come up with a better representation of numbers.
                  We can have a better representation (i.e. one that's a bijection) simply by eliminating all numerals which end in an infinite string of 9's....
                  12-17-10 Mohamed Bouazizi NEVER FORGET
                  Stadtluft Macht Frei
                  Killing it is the new killing it
                  Ultima Ratio Regum

                  Comment


                  • #24
                    If I was as dull as some of you guys, going into deep analysis of the number 1, I believe I would tie myself in a bag and throw me in the river.
                    I wouldn't wait for my dad.
                    Ask Boddington's.
                    Boddington's needs to come home.
                    Life is not measured by the number of breaths you take, but by the moments that take your breath away.
                    "Hating America is something best left to Mobius. He is an expert Yank hater.
                    He also hates Texans and Australians, he does diversify." ~ Braindead

                    Comment


                    • #25
                      Originally posted by alofatti
                      You are not obliged to have o.9999..... equal to 1.
                      You could very well define your own number system where 0.9999... is not 1 (as well it is correctly defined), though perhaps it would share very little resemblance to the real system.
                      I know...and that's why I clarified (after you pointed this out) that what I meant was that the standard representation is not a bijection, not that the two sets aren't bijective (though constructing a bijection would be vaguely difficult...)
                      12-17-10 Mohamed Bouazizi NEVER FORGET
                      Stadtluft Macht Frei
                      Killing it is the new killing it
                      Ultima Ratio Regum

                      Comment


                      • #26
                        Originally posted by SlowwHand
                        If I was as dull as some of you guys, going into deep analysis of the number 1, I believe I would tie myself in a bag and throw me in the river.
                        I wouldn't wait for my dad.
                        Ask Boddington's.
                        Boddington's needs to come home.
                        Man, the number 1 is the most interesting number out there.
                        12-17-10 Mohamed Bouazizi NEVER FORGET
                        Stadtluft Macht Frei
                        Killing it is the new killing it
                        Ultima Ratio Regum

                        Comment


                        • #27
                          I had to look up the 1-to-1 and onto terms, since I've always been told they were injective and surjective instead.
                          "The issue is there are still many people out there that use religion as a crutch for bigotry and hate. Like Ben."
                          Ben Kenobi: "That means I'm doing something right. "

                          Comment


                          • #28
                            Actually, it is interesting to notice that lots of things are studied around the number 1.
                            For example, the fact that 0 < 1 requieres a formal proof, which is not obvious (but also not that hard, though).

                            Comment


                            • #29
                              Quoted from Frogger:
                              "Under the standard decimal representation of the real numbers, every real number has a decimal representation (i.e. Decimal->Real is onto). Unfortunately, the representation is not a bijection, as 0.999999999.... and 1 are both mapped to the same real number. "

                              Not necessarily. One could easily define a map between two sets as he wants to. I am not obliged to send 0.9999... to 1. In terms of cardinality, both sets have the same cardinal. There is a bijection between these sets (which does not send 0.999... and 1 to 1 because that would not be inyective).

                              Quoted from Frogger:
                              "BTW, when you use the word "complete", most people use the word "closed" to represent a set which contains all of its limit points. And the set of reals and the set of decimal reps are both closed"

                              Well, in metrics spaces "closed" is weaker than "complete" (i.e., a space which is complete is closed), but you are right: both sets are closed (in fact, they are complete).

                              Comment


                              • #30
                                alofatti: What do you do for a living?
                                "The issue is there are still many people out there that use religion as a crutch for bigotry and hate. Like Ben."
                                Ben Kenobi: "That means I'm doing something right. "

                                Comment

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