\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
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\begin{document}
\begin{equation*}
  \aligned 
    H_{k+1} &= H_{k} + b_r(u) H_{k} - a L_{k} H_{k} \\
    L_{k+1} &= L_{k} - d_f L_{k} + a L_{k} H_{k},
  \endaligned
\end{equation*}
\end{document}