\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  g_{st} =
  e^{\widehat{\xi}_{11}\theta_{11}} \cdots e^{\widehat{\xi}_{1n_1}\theta_{1n_1}} g_{st}(0) =
  e^{\widehat{\xi}_{21}\theta_{21}} \cdots e^{\widehat{\xi}_{2n_2}\theta_{2n_2}} g_{st}(0),
\end{equation*}
\end{document}