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skulblaka@sh.itjust.works ⁨4⁩ ⁨months⁩ ago

Sure, when you start decoupling the numbers from their actual values. The only thing this proves is that the fraction-to-decimal conversion is inaccurate. Your floating points (and for that matter, our mathematical model) don’t have enough precision to appropriately model what the value of 7/9 actually is. The variation is negligible though, and that’s the core of this, is the variation off what it actually is is so small as to be insignificant and, really undefinable to us - but that doesn’t actually matter in practice, so we just ignore it or convert it. But at the end of the day 0.999… does not equal 1. A number which is not 1 is not equal to 1. That would be absurd. We’re just bad at converting fractions in our current mathematical understanding.

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myslsl@lemmy.world ⁨4⁩ ⁨months⁩ ago
You are just wrong.

The rigorous explanation for why 0.999…=1 is that 0.999… represents a geometric series of the form 9/10+9/10^2+… by definition, i.e. this is what that notation literally means. The sum of this series follows by taking the limit of the corresponding partial sums of this series (see here) which happens to evaluate to 1 in the particular case of 0.999… this step is by definition of a convergent infinite series.

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barsoap@lemm.ee ⁨4⁩ ⁨months⁩ ago

The only thing this proves is that the fraction-to-decimal conversion is inaccurate.

No number is getting converted, it’s the same number in both cases but written in a different representation. 4 is also the same number as IV, no conversion going on it’s still the natural number elsewhere written S(S(S(S(Z)))). Also decimal representation isn’t inaccurate, it just happens to have multiple valid representations of the same number.

A number which is not 1 is not equal to 1.

Good then that 0.999… and 1 are not numbers, but representations.

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- bitfucker@programming.dev ⁨4⁩ ⁨months⁩ ago
  Lol I fucking love that successor of zero
  
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IntriguedIceberg@lemmy.world ⁨4⁩ ⁨months⁩ ago
It still equals 1, you can prove it without using fractions: x = 0.999… 10x = 9.999… 10x = 9 + 0.999… 10x = 9 + x 9x = 9 x = 1

There’s even a Wikipedia page on the subject

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- Clinicallydepressedpoochie@lemmy.world ⁨4⁩ ⁨months⁩ ago
  I hate this because you have to subtract .99999… from 10. Which is just the same as saying 10 - .99999… = 9
  
  Which is the whole controversy but you made it complexicated.
  
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  - Laser@feddit.org ⁨4⁩ ⁨months⁩ ago
    You don’t subtract from 10, but from 10x0.999… I mean your statement is also true but it just proves the point further.
    
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    Clinicallydepressedpoochie@lemmy.world ⁨4⁩ ⁨months⁩ ago
    No you do subtract from 9.999999…
    
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- ColeSloth@discuss.tchncs.de ⁨4⁩ ⁨months⁩ ago
  Do that same math, but use .5555… instead of .9999…
  
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  - BeardedGingerWonder@feddit.uk ⁨4⁩ ⁨months⁩ ago
    Have you tried it? You get 0.555… which kinda proves the point does it not?
    
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  - Wandering_Uncertainty@lemmy.world ⁨4⁩ ⁨months⁩ ago
    ???
    
    Not sure what you’re aiming for. It proves that the setup works, I suppose.
    
    x = 0.555…
    
    10x = 5.555…
    
    10x = 5 + 0.555…
    
    10x = 5+x
    
    9x = 5
    
    x = 5/9
    
    5/9 = 0.555…
    
    So it shows that this approach will indeed provide a result for x that matches what x is supposed to be.
    
    Hopefully it helped?
    
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tuna@discuss.tchncs.de ⁨4⁩ ⁨months⁩ ago
If they aren’t equal, there should be a number in between that separates them. Between 0.1 and 0.2 i can come up with 0.15. Between 0.1 and 0.15 is 0.125. You can keep going, but if the numbers are equal, there is nothing in between.

What number comes between 0.999… and 1?

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IsoSpandy@lemm.ee ⁨4⁩ ⁨months⁩ ago
My brother. You are scared of infinities. Look up the infinite hotel problem. I will lay it out for you if you are interested.

Image you are incharge of a hotel and it has infinite rooms. Currently your hotel is at full capacity… Meaning all rooms are occupied. A new guest arrives. What do you do? Surely your hotel is full and you can’t take him in… Right? WRONG!!! You tell the resident of room 1 to move to room 2, you tell the resident of room 2 to move to room 3 and so on… You tell the resident of room n to move to room n+1. Now you have room 1 empty

But sir… How did I create an extra room? You didn’t. The question is the same as asking yourself that is there a number for which n+1 doesn’t exist. The answer is no… I can always add 1.

Infinity doesn’t behave like other numbers since it isn’t technically a number.

So when you write 0.99999… You are playing with things that aren’t normal. Maths has come with fuckall ways to deal with stuff like this.

Well you may say, this is absurd… There is nothing in reality that behaves this way. Well yes and no. You know how the building blocks of our universe obey quantum mechanics? The equations contain lots of infinities but only at intermediate steps. You have to “renormalise” them to make them go away. Nature apparently has infinities but likes to hide the from us.

The infinity problem is so fucked up. You know the reason physics people are unable to quantize gravity? Surely they can do the same thing to gravity as they did to say electromagnetic force? NOPE. Gravitation doesn’t normalise. You get left with infinities in your final answer.

Anyways. Keep on learning, the world has a lot of information and it’s amazing. And the only thing that makes us human is the ability to learn and grow from it. I wish you all the very best.

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- barsoap@lemm.ee ⁨4⁩ ⁨months⁩ ago
  
  But sir… How did I create an extra room? You didn’t.
  
  When Hilbert runs the hotel, sure, ok. Once he sells the whole thing to an ultrafinitist however you suddenly notice that there’s a factory there and all the rooms are on rails and infinity means “we have a method to construct arbitrarily more rooms”, but they don’t exist before a guest arrives to occupy them.
  
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frezik@midwest.social ⁨4⁩ ⁨months⁩ ago
It’s a correct proof.

One way to think about this is that we represent numbers in different ways. For example, 1 can be 1.0, or a single hash mark, or a dot, or 1/1, or 10/10. All of them point to some platonic ideal world version of the concept of the number 1.

What we have here is two different representations of the same number that are in a similar representation. 1 and 0.999… both point to the same concept.

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Tlaloc_Temporal@lemmy.ca ⁨4⁩ ⁨months⁩ ago
I strongly agree with you, and while the people replying aren’t wrong, they’re arguing for something that I don’t think you said.

1/3 ≈ 0.333… in the same way that approximating a circle with polygons of increasing side number has a limit of a circle, but will never yeild a circle with just geometry.

0.999… ≈ 1 in the same way that shuffling infinite people around an infinite hotel leaves infinite free rooms, but if you try to do the paperwork, no one will ever get anywhere.

Decimals require you to check the end of the number to see if you can round up, but there never will be an end. Thus we need higher mathematics to avoid the halting problem. People get taught how decimals work, find this bug, and then instead of being told how decimals are broken, get told how they’re wrong for using the tools they’ve been taught.

If we just accept that decimals fail with infinite steps, the transition to new tools would be so much easier, and reflect the same transition into new tools in other sciences. Like Bohr’s Atom, Newton’s Gravity, Linnaean Taxonomy, or Comte’s Positivism.

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- barsoap@lemm.ee ⁨4⁩ ⁨months⁩ ago
  
  Decimals require you to check the end of the number to see if you can round up, but there never will be an end.
  
  The character sequence “0.999…” is finite and you know you can round up because you’ve got those three dots at the end. I agree that decimals are a shit representation to formalise rational numbers in but it’s not like using them causes infinite loops. Unless you insist on writing them, that is. You can compute with infinities just fine as long as you either a) bound them or b) keep them symbolic.
  
  That only breaks down with the reals where equality is fundamentally incomputable. Equality of the rationals and approximate equality of reals is perfectly computable though, the latter meaning that you can get equality to arbitrary, but not actually infinite, precision.
  
  …sometimes I do think that all those formalists with all those fancy rules about fancy limits are actually way more confused about infinity than freshman CS students.
  
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  - Tlaloc_Temporal@lemmy.ca ⁨4⁩ ⁨months⁩ ago
    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.
    
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    barsoap@lemm.ee ⁨4⁩ ⁨months⁩ ago
    Noone in the right state of mind uses decimals as a formalisation of numbers, or as a representation when doing arithmetic.
    
    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 bid 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.
    
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    apolo399@lemmy.world ⁨4⁩ ⁨months⁩ ago
    The system works perfectly, it just looks wonky in base 10. In base 3 0.333… looks like 0.1, exactly 0.1
    
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- skulblaka@sh.itjust.works ⁨4⁩ ⁨months⁩ ago
  That does very accurately sum up my understanding of the matter, thanks. I haven’t been adding on to any of the other conversation in order to avoid putting my foot in my mouth further, but you’ve pretty much hit the nail on the head here. And the higher mathematics required to solve this halting problem are beyond me.
  
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