% Skupina rovnic v eqnarray s jednym cislom
% --------------------------------------------
% 21.09.2003
% --------------------------------------------
% Niekedy je potrebne oznacit skupinu rovnic
% (napr. sustavu rovnic) jedinym cislom. 
% Riesenie: vlozit do prostredia equation prostredie 
% array. Je vsak potrebne zvacsit priestor medzi
% rovnicami (t. j. medzi riadkami v array-i).
%
% Popis \arraystretch:
% \arraystretch line spacing in array and tabular
% environments is done by placing a strut in every 
% row of height and depth \arraystretch times the 
% height and depth of the strut produced by an 
% ordinary \strut commmand.
% 
% Zvacsime ho cez \renewcommand{\arraystretch}{1.2}

\documentclass{article}
\usepackage{slovak}
\begin{document}
Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
\begin{equation}
\renewcommand{\arraystretch}{1.2}
\begin{array}{rcl}
2 + 3 & = & 3 + 2\\
x^2 + 2xy + y^2 & = & (x+y)^2\\
(a+b)\cdot (a^2 + ab + b^2) & = & (a^3 + b^3)
\end{array}
\end{equation}

Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
Lorem ipsum dolor sit amet nummy et clara voca lunea hospes.
\begin{eqnarray*}
2 + 3 & = & 3 + 2\\
x^2 + 2xy + y^2 & = & (x+y)^2\\
(a+b)\cdot (a^2 + ab + b^2) & = & (a^3 + b^3)
\end{eqnarray*}

\begin{eqnarray}
  \lefteqn{\int_0^\infty x + y dx =} \\
  & & x + y \\
 a & = & z + t + q
\end{eqnarray}
\end{document}