These last few days we've suddenly seen huge numbers of instances of things like this: Where it was be appropriate to write $f(x) = a_n x^n + \cdots + a_0$, people instead write f(x) = a$_n$x$^n$ +...+a$_0$. Click on "edit" and look at how that's coded! The subscripts and superscripts are in TeX; the "+" and "=" and "f(x)" and "a" and "..." are not. Or they write $a$ + $b$ = $c$ instead of $a+b=c$, again leaving "+" and "=" outside of TeX. All sorts of variations on this theme.
Here's my suspicion: Suddenly people are getting directed to some software somewhere on the web that purports to do things like this for them without their knowing TeX. And it was designed by illiterates who can't spell. If this site is somehow tacitly condoning this, maybe something should be done about it.