如何改变公式中希腊字母的字体大小？

Question

\documentclass[20pt]{beamer}  
\geometry{ papersize = {27cm, 21cm}}  
 \usepackage[english]{babel}  
 \usepackage{mathrsfs, booktabs, multirow}  
 \usepackage{amsmath}  
 \usetheme{Darmstadt}  

\begin{document}  
\begin{frame}  
 \frametitle{Maxwell Equation}\linespread{0.5}  

\huge  

\begin{equation}  
\vec A = \frac{\mu}{4\pi }\int_V {\frac{{\vec J(\vec x')dV'}}{r}}   
\end{equation}  
\begin{equation}  
\nabla \cdot \vec D =\rho  
\end{equation}  
\end{frame}  
\end{document}  

我知道这个问题与有关\huge。拉丁字母和希腊字母的增加比例不同，但如何解决呢？

Answer 1

现在注释掉的前两行是问题的根源。水平间距已dV'更正。

%\documentclass[20pt]{beamer}  
\documentclass{beamer}  
%\geometry{ papersize = {27cm, 21cm}}  
 \usepackage[english]{babel}  
 \usepackage{mathrsfs, booktabs, multirow}  
 \usepackage{amsmath}  
 \usetheme{Darmstadt}  

\begin{document}  
\begin{frame}  
 \frametitle{Maxwell Equation}\linespread{0.5}  

\huge  

\begin{equation}  
%\vec A = \frac{\mu}{4\pi }\int_V {\frac{{\vec J(\vec x')dV'}}{r}}   
\vec A = \frac{\mu}{4\pi }\int_V {\frac{{\vec J(\vec x')\,dV'}}{r}}   
\end{equation}  
\begin{equation}  
\nabla \cdot \vec D =\rho  
\end{equation}  
\end{frame}  
\end{document}