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.
0.999… has no smallest digit, thus the carry operation fails to roll it over to 1.
That’s where limits get involved, snatching the carry from the brink of infinity. You could, OTOH, also ignore that and simply accept that it has to be the case because 0.333… * 3. And let me emphasise this doubly and triply: That is a correct mathematical understanding. You don’t need to get limits involved. It doesn’t make it any more correct, or detailed, or anything. Glancing at Occam’s razor, it’s even the preferable explanation: There’s a gazillion overcomplicated and egg-headed ways to write 1 + 1 = 2 (just have a look at the Principia Mathematica), that doesn’t mean that a kindergarten student doesn’t understand the concept correctly. Begone, superfluous sophistication!
(I just noticed that sophistication actually shares a root with sophistry. What a coincidence)
Someone using only basic arithmetic on decimal notation will conclude that 0.999… is not 1.
Doesn’t pass scrutiny, because then either 0.333… /= 1/3 or 3 /= 3 (or both). It simply cannot be the case when looking at the whole system, as opposed to only the single question 0.999… ?= 1 and trying to glean something from that. Context matters: Any answer to that question has to be consistent with all the rest you know about the natural numbers. And only 0.999… = 1 fulfils that.
Why are you making this so complicated?
simply accept that it has to be the case because 0.333… * 3. […] That is a correct mathematical understanding
This is my point, using a simple system (basic arithmetic) properly will give bad answers in specifically this situation. A correct mathematical understanding of arithmetic will lead you to say that something funky is going on with 0.999… , and without a more comprehensive understanding of mathematical systems, the only valid conclusions are that 0.999… doesn’t equal 1, or that basic arithmetic is limited.
So then why does everyone loose their heads when this happens? Thousands of people forcing algebra and limits on anyone they so much as suspect could have a reasonable but flawed conclusion, yet this thread is the first time I’ve seen anyone even try to mention the limitations of arithmetic, and they get stomped on.
Why is basic arithmetic so sacred that it must not be besmirched? Why is it so hard for people to admit that some tools have limits? Why is everyone bringing in so many more advanced systems when my entire argument this whole time is that a simple system has limits?
That’s my whole argument. Firstly, that 0.999… catches people because using arithmetic properly leads to an incorrect understanding of repeating decimals. And secondly, that starting with the limits of arithmetic will increase understand with less frustration than throwing more complicated solutions around.
My argument have never been with the math, only with our perceptions of it and how we go about teaching it.
