# How do I type the infinity symbol in MacTex? [duplicate]

\item Obtain the one-to-one function $f_1$ and $f_2$ by cutting the graph of $f$ at
a certain point ($x_1$, $y_1$) so that domain of ($f_1$)=($-∞$ , $x_1$] and
domain ($f_2$)=[$x_1$,$+∞$)

• You need \infty – percusse Sep 18 '13 at 15:00
• When using XeLaTeX or LuaLaTeX as your typesetter, you need to include the »unicode-math« package. – Thorsten Donig Sep 18 '13 at 15:07
• Just a general tip: It's safter to use $$f_1$$ and $f_1$ than $f_1$ and $$f_1$$. For more information, see this question: tex.stackexchange.com/questions/503/why-is-preferable-to or read about it in l2tabu. – Sam Whited Sep 18 '13 at 15:11
• @SamWhited -- I would disagree with you on the claim that there's a generic safety related advantage to using $$...$$ rather than $...$ to delimit inline math. Indeed, since $$and $$ are not "robust" commands (in the LaTeX sense of the word "robust"), it's perilous to use them in the arguments of "moving" commands; no such difficulties arise with $. Note that the link you provide regards the use of $$ -- a rather different matter. – Mico Sep 18 '13 at 15:58 • @Mico Fair point; l2tabu doesn't mention  either, though I had thought it talked about line spacing a bit. Oh well, ignore my comment (although I'd still go with the LaTeX way unless you need to put it in a moving argument for some reason). – Sam Whited Sep 18 '13 at 16:20 ## 2 Answers A better style is: Obtain the one-to-one function $f_1$ and $f_2$ by cutting the graph of $f$ at a certain point $(x_1, y_1)$ so that domain of $(f_1)=(-\infty , x_1]$ and domain $(f_2)=[x_1,+\infty)$ (Please compare the obtained spacing). If you are still faced with such a problem, as the last resort, you can use the rotated eight as follows. \documentclass[preview,border=12pt]{standalone} \usepackage{graphicx} \def\infinity{\rotatebox{90}{8}} \begin{document}$(-\infinity, x_1]\$
\end{document}


• Only meticulous readers will spot the difference. – kiss my armpit Sep 18 '13 at 15:38
• Every good math font has the symbol corresponding to \infty. – egreg Sep 18 '13 at 15:44
• @egreg: Yes. It is just for emergency purposes. :-) – kiss my armpit Sep 18 '13 at 15:47
• Some fonts have a \infty that really looks like a rotated 8 instead of a distinct design. – lblb Oct 14 '17 at 15:48