答案1
有一个\splitfrac
命令 from mathtools
,它就是为此而设计的:
\documentclass[a4paper, 12pt]{report}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools}
\begin{document}
\mbox{}
\begin{equation}
A = \left\{\varepsilon_G b +\dfrac{\varepsilon_{HG} bK[H]_t}{\splitfrac{1+0.5\big(-(1-K[G]_t +K[H]_t)}{ + √{(1-K[G]_t +K[H]_t)² + 4K[G]_t}\big)}}\right\}%
\end{equation}
\end{document}