\documentclass[12pt]{article}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\RequirePackage{amsmath,amssymb,latexsym}
\pagestyle{empty}
\begin{document}
$  \dfrac{A_{1}}{A_{2}}=\dfrac{B_{1}}{B_{2}}=\dfrac{C_{1}}{C_{2}}\neq\dfrac{D_{1}}{D_{2}}  $
\end{document}
