\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{align}
        d_r &= k_r,                         \\
  d_{r - 1} &= k_r + k_{r - 1},             \\
  d_{r - 2} &= k_r + k_{r - 1} + k_{r - 2}.
\end{align}

\end{document}