\documentclass{article}
\usepackage{amsmath}

\begin{document}
$$1 + 1 = 2$$
\begin{align}
7 + 5 &= 12\\
12 &= 11 + 1
\end{align}
\end{document}


Can one adjust the skip between the first and second equation to equal that between the second and third?

• I would advise against chaining equation-like environments. – 1010011010 Feb 10 '16 at 17:49

Here is an unorthodox solution: insert an align environment in a gather environment. I don't know if there are any side effects, in particular with cross-references. The orthodox way would be to group the aligned equations within an … aligned environment, but there will be one number for both. With the code you posted, the result is particularly unaesthetic, but I suppose the real equations will be somewhat different:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{gather}
1 + 1 = 2\\
\begin{align}
7 + 5 &= 12\\
12 &= 11 + 1
\end{align}
\end{gather}

\begin{gather}
1 + 1 = 2\\
\begin{aligned}
7 + 5 &= 12\\
12 &= 11 + 1
\end{aligned}
\end{gather}

\end{document}


• There is a problem, though, if one labels equations 2 and 3. – Toothrot Feb 10 '16 at 18:58
• In the first solution, I guess? That's what I said: I didn't test any possible side-effects – Bernard Feb 10 '16 at 19:03

Not in the manual, but, hey, it works!

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\multispan{2}\hfill$\displaystyle 1 + 1 = 2$\hfill \label{A} \\
7 + 5 &= 12+1-1+1-1+1-1+1-1 \label{B} \\
12 &= 11 + 1 \label{C}
\end{align}
Equations \eqref{A}, \eqref{B} and \eqref{C}

\end{document}


• I'm sorry, I should have made my exsample less minimal and more like what I am actually doing. see new quæstion, where the first æquation is split. – Toothrot Feb 10 '16 at 19:16
• @egreg: (+1) I didn't know that one! Is it documented somewhere? – Bernard Feb 10 '16 at 19:54
• @Bernard Under “very very dirty tricks”. – egreg Feb 10 '16 at 20:31