# Gather vs aligned - centered equation with one number

What is the way to achieve something between gather and aligned?

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[utf8]{inputenc}

\begin{document}
\begin{gather}
3(a-x) = 3.5x + a - 1 \\
3a - 3x = 3.5x + a -1 \\
a = \frac{13}{4}x - \frac{1}{2}
\end{gather}

\begin{aligned} 3(a-x) = 3.5x + a - 1 \\ 3a - 3x = 3.5x + a -1 \\ a = \frac{13}{4}x - \frac{1}{2} \end{aligned}
\end{document}


Result:

But... How to achieve something like this? I'd like to keep the centering.

Is this possible somehow?

The gathered environment, used within math mode, is what you're looking for.

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[utf8]{inputenc}
\begin{document}
$$\begin{gathered} 3(a-x) = 3.5x + a - 1 \\ 3a - 3x = 3.5x + a - 1 \\ a = \frac{13}{4}x - \frac{1}{2} \end{gathered}$$
\end{document}


Wikibooks LaTeX has a fairly nice list of the different kinds of equation and align environments.

• This works great, but the numbering is put at the bottom if the equation is too big. Is there a way to force the number to be on the center (right)? – Guilherme Salomé Jun 21 '18 at 15:07