LaTeX multiple equation references in one

This is a simple solution that requires no additional packages, just one additional label:

\begin{subequations}
 \label{eq1}
 \begin{align}
  a & = b \label{eq11} \\
  c & = d \label{eq12}
 \end{align}
\end{subequations}

And when you do \eqref{eq1} it will display as (1).