Several \begin{equation} \end{equation} in columns

Question

I have 3 elements of the following form (approx ~20 equations for each one) :

\begin{equation}
\begin{aligned}
% LOTS OF EQUATIONS %
\end{aligned}
\end{equation}

How to put display these 3 elements in 3 columns on one page ?

I tried :

\begin{tabular}{ccc}
\begin{equation}
\begin{aligned}
% LOTS OF EQUATIONS %
\end{aligned}
\end{equation}
&
\begin{equation}
\begin{aligned}
% LOTS OF EQUATIONS %
\end{aligned}
\end{equation}
&
\begin{equation}
\begin{aligned}
% LOTS OF EQUATIONS %
\end{aligned}
\end{equation}
\end{tabular}

But it does not work and return the following error :

 You can't use '\eqno' in restricted horizontal mode

How to do what I want to do?

Answer 1

You need to hide the alignment operators of the amsmath environments - & and \\ - from tabular. Do this by grouping the content (placing it inside {...}). Here's a minimal example showing its use inside a tabularx environment (it's just easier to spread it across the \linewidth equally this way):

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\usepackage{tabularx}% http://ctan.org/pkg/tabularx
\begin{document}
\noindent
\begin{tabularx}{\linewidth}{@{}XXX@{}}
  {\begin{align}
    y&=17x  \\ y&=7x  \\ y&=12x  \\ y&=14x  \\ y&=1x  \\ y&=8x  \\ y&=9x  \\ y&=5x  \\ y&=11x  \\ y&=16x  \\
    y&=18x  \\ y&=3x  \\ y&=13x  \\ y&=4x  \\ y&=2x  \\ y&=15x  \\ y&=6x  \\ y&=19x  \\ y&=10x  \\ y&=20x
  \end{align}} &
  {\begin{align}
    y&=17x  \\ y&=7x  \\ y&=12x  \\ y&=14x  \\ y&=1x  \\ y&=8x  \\ y&=9x  \\ y&=5x  \\ y&=11x  \\ y&=16x  \\
    y&=18x  \\ y&=3x  \\ y&=13x  \\ y&=4x  \\ y&=2x  \\ y&=15x  \\ y&=6x  \\ y&=19x  \\ y&=10x  \\ y&=20x
  \end{align}} &
  {\begin{align}
    y&=17x  \\ y&=7x  \\ y&=12x  \\ y&=14x  \\ y&=1x  \\ y&=8x  \\ y&=9x  \\ y&=5x  \\ y&=11x  \\ y&=16x  \\
    y&=18x  \\ y&=3x  \\ y&=13x  \\ y&=4x  \\ y&=2x  \\ y&=15x  \\ y&=6x  \\ y&=19x  \\ y&=10x  \\ y&=20x
  \end{align}}
\end{tabularx}
\end{document}​