\documentclass[a4paper,12pt]{article}

\usepackage[italian]{babel}
\usepackage[utf8x]{inputenc}
%\usepackage[latin1]{inputenc}

\usepackage{amsmath}


\begin{document}

% esempio di equation

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, 
\begin{equation}
	F(x):= \int_a^x f(x)\,dx,
\end{equation}
adipiscing vitae, felis. Curabitur dictum gravida mauris.
\begin{equation*}
	F(x):= \int_a^x f(x)\,dx,
\end{equation*}
Nam arcu libero, nonummy eget, consectetuer id, vulputate a, magna.


% % vari esempi di matrici
 
 Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit, vestibulum ut, placerat ac, 
 \begin{displaymath}
 	\begin{matrix}
 		1-x & 2 \\
 		3 & 4-x 
 	\end{matrix}
 \end{displaymath}
 adipiscing vitae, felis. Curabitur dictum gravida mauris.
 \begin{displaymath}
 	\begin{pmatrix}
 		1-x & 2 \\
 		3 & 4-x 
 	\end{pmatrix}
 \end{displaymath}
 Nam arcu libero, nonummy eget, consectetuer id, vulputate a, magna.
 \begin{displaymath}
 	\begin{vmatrix}
 		1-x & 2 \\
 		3 & 4-x 
 	\end{vmatrix}
 \end{displaymath}
 Donec vehicula augue eu neque.
 \begin{displaymath}
 	\begin{Vmatrix}
 		1-x & 2 \\
 		3 & 4-x 
 	\end{Vmatrix}
 \end{displaymath}
 Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.
 \begin{equation}
 	\begin{Vmatrix}
 		1-x & 2 \\
 		3 & 4-x 
 	\end{Vmatrix}
 \end{equation}





\end{document}