# Difficult Equation Alignment

I'm having a trouble with equation alignment. I have the following code:

\begin{aligned} a & = b\\ & = c \end{aligned}
\begin{aligned} \sqrt{a v} & = \frac{c d}{e f}\\ & = f \end{aligned}
\begin{aligned} g & = h+l+k+fg\\ & = i \end{aligned}


the problem is that I want to have the equal sign of the three equation env. aligned together AND the numbering of equations precisely like this (i.e. the number between first and second line of each aligned block). Moreover a page brake occur between before the last equation env. How can I do?

You can use split inside align (but only one alignment point is allowed):

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\begin{split}
a         & = b\\
& = c
\end{split} \\
\begin{split}
\sqrt{av} & = \frac{c d}{e f}\\
& = f
\end{split} \\
\begin{split}
g         & = h+l+k+fg\\
& = i
\end{split}
\end{align}

\end{document}


When the document is in its final form and you need to break such a display, add \displaybreak before the \\ item after which you need the page break.

A combination of align and \mathllap might do the trick. \allowdisplaybreaks enables page breaking between lines in an align (and gather).

\documentclass{article}
\usepackage{mathtools}
\allowdisplaybreaks
\begin{document}
\begin{align}
&\begin{aligned}
\mathllap{a} & = b\\
& = c
\end{aligned} \\
&\begin{aligned}
\mathllap{\sqrt{av}} & = \frac{c d}{e f}\\
& = f
\end{aligned} \\
&\begin{aligned}
\mathllap{g} & = h+l+k+fg\\
& = i
\end{aligned}
\end{align}
\end{document}