Horizontal array of enumerated equations

Question

This is for use in work assignments for math students. I'd like to post multiple parts for a given question, without sacrificing too much space for this. So I want a bunch of equations arrayed horizontally. Each equation should be labeled as a), b) and so on. The labels should be aligned with the top of (the largest of) the boxes. And it would be nice if the space between equations were maximized to fill the whole width of the page.

At the moment, I use a single align* environment, with the spacing between colums that this provides. I use a \raisebox with a manually tuned length to create place the labels in front of each. I haven't managed to span the whole width yet. The result looks like this:

I thought that maybe the adjustbox package might be able to help me automate the vertical alignment, and allow me to put \hfill between boxes to use the whole width, but so far I haven't managed to get my equations into such boxes.

Do you have any experience in putting display math into an adjustbox?
Do you know of any other package or environment which might help me in this task?

Answer 1

The flalign environment, with some help if you want a padding on either side show to be useful; I have hardcode \footnotesize for the matrices, it's easily modifiable.

\documentclass{article}
\usepackage{geometry}
\usepackage{amsmath,adjustbox}
\usepackage{lipsum} % just for the example

\newenvironment{exercise}[1]
 {\text{#1) }
  \begin{adjustbox}{valign=t}\footnotesize$\displaystyle}
 {$\end{adjustbox}}


\begin{document}
\lipsum*[2]
\begin{flalign*}
\quad&
\begin{exercise}{a}
\begin{pmatrix}
3 & 4 & 1 & 3\\
2 & 1 & 2 & 1\\
2 & 6 &-2 & 1\\
5 & 5 & 2 & 3
\end{pmatrix}
\cdot x =
\begin{pmatrix}
3\\9\\-9\\11
\end{pmatrix}
\end{exercise}
&&
\begin{exercise}{b}
\begin{pmatrix}
3 & 3 & 0 & 0\\
2 & 4 & 2 & 0\\
5 & 4 &-1 & 0\\
3 & 6 & 1 & 2
\end{pmatrix}
\cdot x =
\begin{pmatrix}
0\\10\\-5\\11
\end{pmatrix}
\end{exercise}
&&
\begin{exercise}{c}
\begin{pmatrix}
2 & 0 & 0 & 2\\
4 & 4 & 0 & 0\\
3 & 2 & 1 &-1\\
5 & 4 & 0 & 1
\end{pmatrix}
\cdot x =
\begin{pmatrix}
2\\0\\3\\1
\end{pmatrix}
\end{exercise}
\quad\\[3ex]
\quad&
\begin{exercise}{d}
\begin{pmatrix}
3 & 4 & 1 & 3\\
2 & 1 & 2 & 1\\
2 & 6 &-2 & 1\\
5 & 5 & 2 & 3
\end{pmatrix}
\cdot x =
\begin{pmatrix}
3\\9\\-9\\11
\end{pmatrix}
\end{exercise}
&&
\begin{exercise}{e}
\begin{pmatrix}
3 & 3 & 0 & 0\\
2 & 4 & 2 & 0\\
5 & 4 &-1 & 0\\
3 & 6 & 1 & 2
\end{pmatrix}
\cdot x =
\begin{pmatrix}
0\\10\\-5\\11
\end{pmatrix}
\end{exercise}
&&
\begin{exercise}{f}
\begin{pmatrix}
2 & 0 & 0 & 2\\
4 & 4 & 0 & 0\\
3 & 2 & 1 &-1\\
5 & 4 & 0 & 1
\end{pmatrix}
\cdot x =
\begin{pmatrix}
2\\0\\3\\1
\end{pmatrix}
\end{exercise}
\quad
\end{flalign*}
\lipsum[3]
\end{document}