\displaystyle for a part of the document
With the etoolbox
and/or enumitem
packages:
\documentclass{article}
\usepackage[showframe, nomarginpar]{geometry}
\usepackage{mathtools}
\usepackage{enumitem}
\usepackage{etoolbox}
\AtBeginEnvironment{enumerate}{\everymath{\displaystyle}}
\begin{document}
\begin{enumerate}%
\item $\sin \frac{1}{x},\quad x\in (0,1]$
\item $\frac{1}{\sin x},\quad x\in \left[\frac{\pi}{6},\frac{5\pi}{6}\right]$
\item $ \frac{x}{\sin x},\quad x\in \left[\frac{\pi}{6},\frac{\pi}{2}\right]$
\end{enumerate}
\end{document}
If you want this just for one environment, you can use this (without etoolbox
) instead:
\begin{enumerate}[before=\everymath{\displaystyle}]
Use \everymath{\displaystyle}
. To make it local, put it inside a group:
\documentclass{article}
\begin{document}
Text style: $\frac{a}{b}$
\bgroup
\everymath{\displaystyle}
Display style: $\frac{a}{b}$
\egroup
And back: $\frac{a}{b}$
\end{document}