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I was curious. Normal Human recently told me that MathJax is the site's syntax. I am well aware of that and figure that it is just being automated. However, I'm curious whether you must use MathJax for representing simple things such as 1+x?

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    $\begingroup$ I would use MathJax even for simple things, as it's not that hard to use and it increases readability by a large degree. $\endgroup$ – cheesyfluff Nov 22 '15 at 4:38
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    $\begingroup$ I use MathJax even for numerals standing alone (e.g. $2$). It really does look nicer, and when you start to write any formula with more than one term (e.g. $1+1$). Plus, it helps differentiate math from words - i.e. writing $x$ instead of x creates more visual separates symbols and text. I wouldn't edit just to make such changes, but anything more left in bare text is problematic (e.g. as Normal Human notes in their answer, something like n(n-1)x^(n-2) is far less readable than $n(n-1)x^{n-2}$) $\endgroup$ – Milo Brandt Nov 22 '15 at 5:31
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    $\begingroup$ You're free to care as little as you'd like about mathematical conventions, such as typesetting mathematics. You can expect a lukewarm reception at best, I would assume, but you're still free to do what you'd like. $\endgroup$ – pjs36 Nov 22 '15 at 6:52
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    $\begingroup$ Some older related questions can be found here and here. This answer is worth reading in connection with this, too. $\endgroup$ – Martin Sleziak Nov 22 '15 at 7:02
  • $\begingroup$ That is very interesting. I never thought of that,although for things like x it's not going to make it easier for an assisting tool, as x is a single letter in it's own right. $\endgroup$ – The Great Duck Nov 22 '15 at 7:12
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    $\begingroup$ TheGreatDuck. An obvious advantage to using MathJax for everything is that then you will use the fonts uniformly. When you start mixing (still relatively simple) things like $x^7+17x^5+e^x$ and 1+x you will leave people wondering, whether $x$ denotes the same variable as x. Fonts (and cases) are occasionally used to indicate different kinds of objects (there are not enough letters for all the things we may need to denote!). So, why try and confuse people whose help you want to enlist? $\endgroup$ – Jyrki Lahtonen Nov 22 '15 at 7:29
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    $\begingroup$ I was making a comment about the voice reader. That's all. I already said I agreed with the font stuff. $\endgroup$ – The Great Duck Nov 22 '15 at 7:29
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    $\begingroup$ To answer the title question: It is encouraged, for semantic reasons, if and only if it is part of the mathematics (no matter if simple or complicated). By contrast, if you'd write: "I will show you 3 different ways to do this." then you should rather not typeset the numeral in MathJax. (Actually in that specific case you really rather should write "three" but just to get the idea across.) Likewise, for numbered lists it is better not to use MathJax for the iterator. $\endgroup$ – quid Nov 22 '15 at 11:28
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    $\begingroup$ As soon as variables and operators are involved, I'd always use MathJax (or TeX for that matter), for single numerals it may depend on usage (i.e, if the numeral is used mathematically): "In 2015 it was discovered that $42$ is not prime. The proof was simply that $42=6\cdot 7$." $\endgroup$ – Hagen von Eitzen Nov 29 '15 at 18:15
  • $\begingroup$ @MiloBrandt Interestingly, I did that and someone edited my question and removed the MathJax I put on the single numbers. $\endgroup$ – zagadka314 Dec 4 '15 at 1:42
  • $\begingroup$ You cared enough to post a meta comment? Either way this goes no one is gonna be bothered to go through old questions for something so trivial. $\endgroup$ – Alec Teal Dec 5 '15 at 16:48
  • $\begingroup$ What are you even talking about @AlecTeal? I didn't say anything about changing old answers. I was just asking if there was a rule about me using it or not because a couple people told me I was supposed to use it. Did you even read my question? $\endgroup$ – The Great Duck Dec 5 '15 at 20:29
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1+2+3+4+5+...+n is a mathematical formula presented as plain text. While it is readable as such, presenting it as $1+2+3+4+5+\cdots+n$ is a more semantic approach, which allows for the structure of the formula to be parsed and presented as mathematical markup (MathML).

I'm not the only one commenting on the formatting of your posts: you received a similar comment on this answer today. And in this recent answer you also presented formulas such as n(n-1)x^(n-2) as plain text. So yes, there is room for improvement.

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In my opinion there's no need to use MathJax as long as one simply mentions a number in the middle of a prose paragraph -- the default text font has prefectly servicable digits that can be used for that.

However, once one progresses to mathematical expressions with symbols in them -- even just for arithmetic such as $+$ and the like -- then MathJax produces nicer text. And then freestanding numbers that are connected to those calculations should be in MathJax too, for consistency. This also goes for variable names. Variable letters ought to be set in italic, and even if the variable is never used in an actual formula, writing $x$ is not much more of a burden than writing _x_.

On the other hand, numbers that are not mentioned as objects of the mathematical discourse might as well be in the plain text font. So I would write, for example,

In 1975, John Doe published a proof that $\pi=4$. Doe acknowledged that most authorities hold that $4$ is too large a value, but argued that they were just jealous of his genius. He released a revised 34-page proof in 1979.

But in a different answer where I need no formulas, I wouldn't hesitate to write

I think my favorite prime is 61, but I also have weak spots for 11, 257, and 2147483647.

without MathJax.

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    $\begingroup$ I'd like to see that proof! $\endgroup$ – Asaf Karagila Nov 22 '15 at 21:21
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    $\begingroup$ @Asaf: too bad it was in the seventies. Today surely it would be posted here. $\endgroup$ – quid Nov 22 '15 at 22:39
  • $\begingroup$ lol that's an awesome proof. $\endgroup$ – The Great Duck Nov 22 '15 at 23:09
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    $\begingroup$ Perhaps less relevant on M.SE, but for typesetting in general, it is certainly advisable to use math mode exactly when your content semantically represents numbers. (This, of course, should come as no surprise.) One practical example of this is detailed in Knuth's "Typesetting Concrete Mathematics". See the bottom of the second column for context, and the middle of the first column on the second page ("Text numerals are used…") for the lesson. In my opinion, this is likewise a good practice to follow everywhere. $\endgroup$ – wchargin Nov 24 '15 at 8:13
  • $\begingroup$ He should have presented the proof to the Indiana legislature. $\endgroup$ – Mars Nov 28 '15 at 5:11
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For "simple listings of numbers" I would say no, it's not required. For example, to list the Fibonacci numbers: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, ... I see this as a trade-off: by not invoking math mode for that listing, your browser displays it faster, but because the default font for regular text on this site is something like Georgia, it doesn't look quite as good as it would look in math mode.

But $1 + x$ is quite a different thing, it's not as simple a thing as a bunch of integers. In addition to a numeric literal, it also involves an arithmetic operator and a variable designated by a letter of the Latin alphabet. Unless you're a political columnist writing a political column, there is no excuse to use regular text for Latin alphabet variables.

It can put up unnecessary roadblocks to reading distinguishing between English words, abbreviations and expressions with tacit multiplication operators. In one of your recent answers, you write "fyi" presumably to mean "for your information." A Sheldonian might wonder if you meant $f \times y \times i$ or $f(y \times i)$ or even (quite implausibly, of course) $\int y \times i$.

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    $\begingroup$ Why aren't you worried how, say, '1337' will be interpreted when not marked up? :-) $\endgroup$ – quid Nov 25 '15 at 16:25
  • $\begingroup$ I just hadn't thought about that. I guess now it will keep me up all night... $\endgroup$ – Robert Soupe Nov 26 '15 at 1:23
  • $\begingroup$ Quids response is $1337$ $\endgroup$ – The Great Duck Nov 26 '15 at 8:30
  • $\begingroup$ For positive numerals, fine. But negative numerals need the dollars, to produce the correct minus-sign, e.g. $-1$. $\endgroup$ – Rosie F Feb 26 at 11:37
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I my point of view, it is good(may be necessory) to use mathjax whenever you are using mathematical expressions.

for example, when i wish to type like $$\text{Let} f \text{ be a function}$$ We must use mathjax for that $f$ also. Why because, if you are normally typing like 'f' this look like the normal text

                                      'f'. 

But if you are typing it inside the dollars like $f$ you will get the result as, $$f$$

Compare the difference,

And similarly,

For variables, numbers, and simple expression you can find the differences in the below table

$\begin{array}{cc} \text{without Mathjax} & \text{With Mathjax}\\ \text{x} & x\\ \text{z} & z\\ \text{1+2+3+...} & 1+2+3+\ldots\\ \text{...} & \ldots\\ \text{i.e.,} & i.e., \end{array}$

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    $\begingroup$ Using MathJax to give examples of how things look when not using MathJax is... confusing. $\endgroup$ – user642796 Nov 25 '15 at 9:57
  • $\begingroup$ I mean to say within dollar and without dollars.. $\endgroup$ – David Nov 25 '15 at 10:03
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    $\begingroup$ However your "without MathJax" are not without MathJax. They are inside dollar signs, only with \text{....} wrapped around them too -- which still produces something that looks clearly different from text outside MathJax on this site (at least with all the browser/OS combinations I routinely use). $\endgroup$ – Henning Makholm Nov 25 '15 at 11:36
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    $\begingroup$ In fact, you should not typeset "i.e." using MathJax, more generally MJ is not for italicizing text. $\endgroup$ – quid Nov 25 '15 at 16:22

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