[Tex/LaTex] Equation brackets after frac remain small

bracketsequationsfractions

My brackets in the equation remain small, between brackets I have a fraction, usually the brackets auto size and become the same size and enclose the fraction. 

\documentclass[11pt,a4paper]{report}
\usepackage{graphicx}
\usepackage[a4paper]{geometry}
\usepackage[english]{babel}
\usepackage{fancyhdr}
\usepackage{float}
\usepackage{epstopdf}
\usepackage{enumerate}
\usepackage[utf8]{inputenc}
\usepackage{pdfpages}
\usepackage{tabularx}
\usepackage{array}
\usepackage{amsmath}
\begin{document}
\begin{equation}\label{eqn:arr}
k(T)=k^0\texttt{exp}(\frac{E}{R}(\frac{1}{T_{ref}})-\frac{1}{T})
\end{equation}
\end{document}

Best Answer

Brackets in equations only auto size if you ask them to. You can either set the size manually with \big, \Big, \bigg or \Bigg or let LaTeX compute it for you with \left(…\right). You need to use the former if the latter gives the wrong sizes or fails to compile, e.g. if you have brackets across several lines or some form of \underbrace. In your case,

\begin{equation}\label{eqn:arr}
k(T)=k^0\texttt{exp}\left(\frac{E}{R}\left(\frac{1}{T_{ref}}\right)-\frac{1}{T}\right)
\end{equation}
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