\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  \frac{dx}{dt}=\lambda -\mu=\lambda -\mu_\text{max}f(x),\quad x\geq 0,
\end{equation*}
\end{document}