Aligning two multiline equations

Question

I searched a lot for this but couldn't find an answer. Say I have two equations that are 2 lines long each. I can align each equation at their equality sign using equation-aligned or gather-split, like this:

\begin{gather}
\begin{split}
  a &=b \\
    &=c
\end{split}
\\
\begin{split}
  k &=l+55 \\
    &=d+401
\end{split}
\end{gather}

However, I can't find a way to align the equality signs of both sets of code. Any solutions?

Answer 1

Just change gather into align:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\begin{split}
  a &=b \\
    &=c
\end{split}
\\
\begin{split}
  k &=l+55 \\
    &=d+401
\end{split}
\end{align}

\end{document}

If you pass the tbtags option to amsmath, you get the equation numbers aligned with the bottom line instead of centered on the split.

\documentclass{article}
\usepackage[tbtags]{amsmath}

\begin{document}

\begin{align}
\begin{split}
  a &=b \\
    &=c
\end{split}
\\
\begin{split}
  k &=l+55 \\
    &=d+401
\end{split}
\end{align}

\end{document}