Skip Navigation

You're viewing part of a thread.

Show Context
231 comments

  • Eh, if you need special rules for 0.999... because the special rules for all other repeating decimals failed, I think we should just accept that the system doesn't work here. We can keep using the workaround, but stop telling people they're wrong for using the system correctly.

    The deeper understanding of numbers where 0.999... = 1 is obvious needs a foundation of much more advanced math than just decimals, at which point decimals stop being a system and are just a quirky representation.

    Saying decimals are a perfect system is the issue I have here, and I don't think this will go away any time soon. Mathematicians like to speak in absolutely terms where everything is either perfect or discarded, yet decimals seem to be too simple and basal to get that treatment. No one seems to be willing to admit the limitations of the system.

    • Noone in the right state of mind uses decimals as a formalisation of numbers, or as a representation when doing arithmetic.

      But the way I learned decimal division and multiplication in primary school actually supported periods. Spotting whether the thing will repeat forever can be done in finite time. Constant time, actually.

      The deeper understanding of numbers where 0.999… = 1 is obvious needs a foundation of much more advanced math than just decimals

      No. If you can accept that 1/3 is 0.333... then you can multiply both sides by three and accept that 1 is 0.99999.... Primary school kids understand that. It's a bit odd but a necessary consequence if you restrict your notation from supporting an arbitrary division to only divisions by ten. And that doesn't make decimal notation worse than rational notation, or better, it makes it different, rational notation has its own issues like also not having unique forms (2/6 = 1/3) and comparisons (larger/smaller) not being obvious. Various arithmetic on them is also more complicated.

      The real take-away is that depending on what you do, one is more convenient than the other. And that's literally all that notation is judged by in maths: Is it convenient, or not.

      • I never commented on the convenience or usefulness of any method, just tried to explain why so many people get stuck on 0.999... = 1 and are so recalcitrant about it.

        If you can accept that 1/3 is 0.333... then you can multiply both sides by three and accept that 1 is 0.99999....

        This is a workaround of the decimal flaw using algebraic logic. Trying to hold both systems as fully correct leads to a conflic, and reiterating the algebraic logic (or any other proof) is just restating the problem.

        The problem goes away easily once we understand the limits of the decimal system, but we need to state that the system is limited! Otherwise we get conflicting answers and nothing makes sense.

        • The problem goes away easily once we understand the limits of the decimal system, but we need to state that the system is limited!

          But the system is not limited: It has a representation for any rational number. Subjectively you may consider it inelegant, you may consider its use in some area inconvenient, but it is formally correct and complete.

          I bet there's systems where rational numbers have unique representations (never looked into it), and I also bet that they're awkward AF to use in practice.

          This is a workaround of the decimal flaw using algebraic logic.

          The representation has to reflect algebraic logic, otherwise it would indeed be flawed. It's the algebraic relationships that are primary to numbers, not the way in which you happen to put numbers onto paper.

          And, honestly, if you can accept that 1/3 == 2/6, what's so surprising about decimal notation having more than one valid representation for one and the same number? If we want our results to look "clean" with rational notation we have to normalise the fraction from 2/6 to 1/3, and if we want them to look "clean" with decimal notation we, well, have to normalise the notation, from 0.999... to 1. Exact same issue in a different system, and noone complains about.

          • Decimals work fine to represent numbers, it's the decimal system of computing numbers that is flawed. The "carry the 1" system if you prefer. It's how we're taught to add/subtract/multiply/divide numbers first, before we learn algebra and limits.

            This is the flawed system, there is no method by which 0.999... can become 1 in here. All the logic for that is algebraic or better.

            My issue isn't with 0.999... = 1, nor is it with the inelegance of having multiple represetations of some numbers. My issue lies entirely with people who use algebraic or better logic to fight an elementary arithmetic issue.

            People are using the systems they were taught, and those systems are giving an incorrect answer. Instead of telling those people they're wrong, focus on the flaws of the tools they're using.

            • This is the flawed system, there is no method by which 0.999… can become 1 in here.

              Of course there is a method. You might not have been taught in school but you should blame your teachers for that, and noone else. The rule is simple: If you have a nine as repeating decimal, replace it with a zero and increment the digit before that.

              That's it. That's literally all there is to it.

              My issue lies entirely with people who use algebraic or better logic to fight an elementary arithmetic issue.

              It's not any more of an arithmetic issue than 2/6 == 1/3: As I already said, you need an additional normalisation step. The fundamental issue is that rational numbers do not have unique representations in the systems we're using.

              And, in fact, normalisation in decimal representation is way easier, as the only case to worry about is indeed the repeating nine. All other representations are unique while in the fractional system, all numbers have infinitely many representations.

              Instead of telling those people they’re wrong, focus on the flaws of the tools they’re using.

              Maths teachers are constantly wrong about everything. Especially in the US which single-handedly gave us the abomination that is PEMDAS.

              Instead of blaming mathematicians for talking axiomatically, you should blame teachers for not teaching axiomatic thinking, of teaching procedure instead of laws and why particular sets of laws make sense.

              That method I described to get rid of the nines is not mathematical insight. It teaches you nothing. You're not an ALU, you're capable of so much more than that, capable of deeper understanding that rote rule application. Don't sell yourself short.

              EDIT: Bijective base-10 might be something you want to look at. Also, I was wrong, there's way more non-unique representations: 0002 is the same as 2. Damn obvious, that's why it's so easy to overlook. Dunno whether it easily extends to fractions can't be bothered to think right now.

              • Maths teachers are constantly wrong about everything

                Very rarely wrong actually.

                the abomination that is PEMDAS

                The only people who think there's something wrong with PEMDAS are people who have forgotten one or more rules of Maths.

              • I don't really care how many representations a number has, so long as those representations make sense. 2 = 02 = 2.0 = 1+1 = -1+3 = 8/4 = 2x/x. That's all fine, we can use the basic rules of decimal notation to understand the first three, basic arithmetic to understand the next three, and basic algebra for the last one.

                0.999... = 1 requires more advanced algebra in a pointed argument, or limits and infinite series to resolve, as well as disagreeing with the result of basic decimal notation. It's steeped in misdirection and illusion like a magic trick or a phishing email.

                I'm not blaming mathematicians for this, I am blaming teachers (and popular culture) for teaching that tools are inflexible, instead of the limits of those systems.

                In this whole thread, I have never disagreed with the math, only it's systematic perception, yet I have several people auguing about the math with me. It's as if all math must be regarded as infinitely perfect, and any unbelievers must be cast out to the pyre of harsh correction. It's the dogmatic rejection I take issue with.

                • 0.999… = 1 requires more advanced algebra in a pointed argument,

                  You're used to one but not the other. You convinced yourself that because one is new or unacquainted it is hard, while the rest is not. The rule I mentioned Is certainly easier that 2x/x that's actual algebra right there.

                  It’s as if all math must be regarded as infinitely perfect, and any unbelievers must be cast out to the pyre of harsh correction

                  Why, yes. I totally can see your point about decimal notation being awkward in places though I doubt there's a notation that isn't, in some area or the other, awkward, and decimal is good enough. We're also used to it, that plays a big role in whether something is judged convenient.

                  On the other hand 0.9999... must be equal to 1. Because otherwise the system would be wrong: For the system to be acceptable, for it to be infinitely perfect in its consistency with everything else, it must work like that.

                  And that's what everyone's saying when they're throwing "1/3 = 0.333.... now multiply both by three" at you: That 1 = 0.9999... is necessary. That it must be that way. And because it must be like that, it is like that. Because the integrity of the system trumps your own understanding of what the rules of decimal notation are, it trumps your maths teacher, it trumps all the Fields medallists. That integrity is primal, it's always semantics first, then figure out some syntax to support it (unless you're into substructural logics, different topic). It's why you see mathematicians use the term "abuse of notation" but never "abuse of semantics".

                  • Again, I don't disagree with the math. This has never been about the math. I get that ever model is wrong, but some are useful. Math isn't taught like that though, and that's why people get hung up things like this.

                    Basic decimal notation doesn't work well with some things, and insinuates incorrect answers. People use the tools they were taught to use. People get told they're doing it wrong. People give up on math, stop trying to learn, and just go with what they can understand.

                    If instead we focus on the limitations of some tools and stop hammering people's faces in with bigger equations and dogma, the world might have more capable people willing to learn.

                    • I get that ever model is wrong, but some are useful.

                      There is nothing wrong about decimal notation. It is correct. There's also nothing wrong about Roman numerals... they're just awkward AF.

                      Basic decimal notation doesn’t work well with some things, and insinuates incorrect answers.

                      You could just as well argue that fractional notation "insinuates" that 1/3 + 1/3 = 2/6. You could argue that 8 + 8 is four because that's four holes there. Lots of things that people can consider more intuitive than the intended meaning. Don't get me started on English spelling.

                      • Neither of those examples use the rules of those system though.

                        Basic arithmetic on decimap notation is performed by adding/subtracting each digit in each place, or multiplying each digit by each digit then adding those sub totals together, or the yet more complicated long division.

                        Adding (and by extension multiplying) requires the carry operation, because digits only go up to 9. A string of 9s requires starting at the smallest digit. 0.999... has no smallest digit, thus the carry operation fails to roll it over to 1. It's a bug that requires more comprehensive methods to understand.

                        Someone using only basic arithmetic on decimal notation will conclude that 0.999... is not 1. Another person using only geocentrism will conclude that some planets follow spiral orbits. Both conclusions are wrong, but the fault lies with the tools, not the people using them.

            • those systems are giving an incorrect answer

              When there's an incorrect answer it's because the user has made a mistake.

              Instead of telling those people they’re wrong

              They were wrong, and I told them where they went wrong (did something to one side of the equation and not the other).

              • The system I'm talking about is elementary decimal notation and basic arithmetic. Carry the 1 and all that. Equations and algebra are more advanced and not taught yet.

                There is no method by which basic arithmetic and decimal notation can turn 0.999... into 1. All of the carry methods require starting at the smallest digit, and repeating decimals have no smallest digit.

                If someone uses these systems as they were taught, they will get told they're wrong for doing so. If we focus on that person being wrong, then they're more likely to give up on math entirely, because they're wrong for doing as they were taught. If we focus on the limitstions of that system, then they have the explanation for the error, and an understanding of why the more complicated system is preferable.

                All models are wrong, but some are useful.

                • not taught yet

                  What do you mean not taught yet? There's nothing in the meme to indicate this is a primary school problem. In fact it explicitly has a picture of an adult, so high school Maths is absolutely on the table.

                  There is no method by which basic arithmetic and decimal notation can turn 0.999… into 1.

                  In high school we teach that they are the same thing. i.e. limits of accuracy, 1 isn't the same thing as 1.000..., but rather 1+/- some limit of accuracy (usually 1/2). Of course in programming it matters if you're talking about an integer 1 or a floating point 1.

                  If someone uses these systems as they were taught, they will get told they’re wrong for doing so

                  The only people I've seen get things wrong is people not using the systems correctly (such as the alleged "proof" in this thread, which broke several rules of Maths and as such didn't prove anything), and it's a teacher's job to point out how to use them correctly.

                  • What do you mean not taught yet?

                    I mean those more advanced methods are taught after basic arithmetic. There are plenty of adults that operate primarily with 5th grade math, and a scary number of them do finances...

                    limits of accuracy

                    This isn't about limits of accuracy, we're working with abstract values and ideal systems. Any inaccuracies must be introduced by those systems.

                    If you think the system isn't at fault here, please show me how basic arithmetic can make 0.999... into 1. Show me how the carry method deals with Infinity correctly. If every error is just using the system incorrectly, then a correct use of the system must be applicable to everything, right? You shouldn't need a new system like algebra to be correct, right?

                    • This isn’t about limits of accuracy

                      According to who? Where does it say what it's about? It doesn't.

                      please show me how basic arithmetic can make 0.999

                      You still haven't shown why you're limiting yourself to basic arithmetic. There isn't anything at all in the meme to indicate it's about basic arithmetic only. It's just some Maths statements with no context given.

                      then a correct use of the system must be applicable to everything, right?

                      Different systems for different applications. Sometimes multiple systems for one problem (e.g. proofs).

                      You shouldn’t need a new system like algebra to be correct, right?

                      Limits of accuracy isn't algebra.

                      • This isn’t about limits of accuracy

                        According to who?

                        According to me, talking about the origin of the 0.999... issue of the original comment, the "conversion of fractions to decimals", or using basic arithmetic to manipulate values into repeating decimals. This has been my position the entire time. If this was about the limits of accuracy, then it would be impossible to solve the 0.999... = 1 issue. Yet it is possible, our accuracy isn't limited in this fashion.

                        You still haven't shown why you're limiting yourself to basic arithmetic.

                        Because that's where the entire 0.999... = 1 originates. You'll never even see 0.999... without using basic addition on each digit individually, especially if you use fractions the entire time. Thus 0.999... is an artifact of basic arithmetic, a flaw of that system.

                        Different systems for different applications.

                        Then you agree that not every system is applicable everywhere! Even if you use that system perfectly, you'll still end up with the wrong answer! Thus the issue isn't someone using the system incorrectly, it's a limitation of the system that they used. The correct response to this isn't throwing heaps of other systems at the person, it's communicating the limit of that system.

                        If someone is trying to hammer a screw, chastising them for their swinging technique then using your personal impact wrench in front of them isn't going to help. They're just going to hit you with the hammer, and continue using the tools they have. Explaining that a hammer can't do the twisting motion needed for screws, then handing them a screwdriver will get you both much farther.

                        Limits of accuracy isn't algebra.

                        It never was, and neither is the problem we've been discussing. You can talk about glue, staples, clamps, rivets, and bolts as much as you like, people with hammers are still going to hit screws.

    • The system works perfectly, it just looks wonky in base 10. In base 3 0.333... looks like 0.1, exactly 0.1

      • Oh the fundamental math works fine, it's the imperfect representation that is infinite decimals that is flawed. Every base has at least one.

231 comments