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I don't usually use that term, but I take it to mean "number you (may, and, if not using e.g. fractions, must) write using a decimal point" because that seems t
by yamtaddle 3y ago
I don't usually use that term, but I take it to mean "number you (may, and, if not using e.g. fractions, must) write using a decimal point" because that seems to always be what people intend by it.
Everybody experienced writing irrational numbers using decimal notation in school, so those definitely count.
- xigoi 3y agoThe correct mathematical term is “real number”.
- yamtaddle 3y agoYes, but you'll see "decimal" more in the wild, and that's what people mean by it. "You write it with a decimal point", and they do usually mean to include the irrationals. So, yes, real numbers, but the reasoning behind their usage is "you write it with a decimal point". I'd bet more people understand "decimal number" used in that sense, than understand "real number".
- bombolo 3y agoi've never seen an irrational number written in digits in my whole life. Have you????? I've seen them expressed as letters or formule
- yamtaddle 3y agoNever. Never in school? It's totally normal in the US, it's the reason as many people know that π starts "3.14" as do.
- bombolo 3y agoYes never, not in school, not in analysis, and certainly not in numerical analysis. You've proved my point. It's either π or 3.14. Except that the latter is a rational number :)
- yamtaddle 3y ago> Yes never, not in school, not in analysis, and certainly not in numerical analysis. Weird, I just assumed that was normal in most education systems. I don't know how you'd get a sense of the rough scale of various common irrationals, without having some idea what they look like when represented in decimal notation. Such representations are normal starting not later than when we start seriously working with circles, in US school, and never really stop coming after that. Estimation exercises lean heavily on having some idea of the decimal representation. > You've proved my point. It's either π or 3.14. Except that the latter is a rational number :) Never claimed π is 3.14, so no, I didn't at all prove your point. I wrote that it's very well known that it starts that way. When a normal person says "decimal number" they mean to include π, because any usefully-precise decimal representation of it's going to involve a decimal point. At least in the US, they saw it represented "3.14..." or "3.1459..." or whatever, many, many times in school. It's obviously, to a non-mathematician, a "decimal number". They mean "the real numbers" (or, perhaps, depending on context, exclusively the parts of the reals that aren't whole integers), except that name is harder to remember than the incorrect (but more common and intuitive) "decimal numbers".
- bombolo 3y agoCan you write here an irrational number, not in the form of a letter or a formula? For me a "decimal number" is a number represented in base 10. Which is why I was asking. I even googled and there is no real definition.
- paulddraper 3y ago3.14...
- bombolo 3y agoIsn't that equal to 157/50?
- someweirdperson 3y ago> i've never seen an irrational number written in digits in my whole life. Have you????? I'm currently reading one. Looking good so far. I'll let you know after I finish.
- Georgelemental 3y ago> Everybody experienced writing irrational numbers using decimal notation in school, To be pedantic, we experienced writing approximations of these numbers in decimal arithmetic.
- School-Cotton 3y agoIt’s not just pedantic! It completely changes the answer to the question.
- yamtaddle 3y agoDo you actually think I meant otherwise? Like, actually? Do you think anyone on HN was confused about it? Did you really think that?
- GreymanTheGrey 3y agoYes, I thought you meant otherwise. Yes, I was confused about it. Yes, I really thought that. Truly.
- yamtaddle 3y agoYou truly thought I didn't realize that "3.14" is an abbreviated representation of π, or that I somehow missed years and years of using the "repeating" sign above various decimal representations, or all those "..."s, such that it was plausible I meant the obviously-wrong thing rather than the correct thing? This stuff is hammered in in US K-12 school. [EDIT] Look, I don't mean to be a dick, performative misreading and plainly-unnecessary "correction" are just two of my least-favorite types of HN post. I probably should have just downvoted the original performative misreading (not yours, the one up-thread) and not Assumed Good Faith that the original poster genuinely doesn't understand what every non-math-nerd means when they say or write "decimal number" (it's the ones you write with a decimal. It's... so very simple, that's why non-math-nerds use that and not "real number", the definition of which they've long since forgotten. "Well but you can't actually represent irrationals them entirely in decimal notation" great, wonderful, has zero bearing on what people mean by it).
- jameshart 3y agoNobody ever finished writing an irrational number in school.