\documentclass[a4paper,11pt]{report}
\usepackage[latin1]{inputenc}
\usepackage[italian]{babel}
\usepackage{graphicx}

\newtheorem{prop}{Proposizione}
\newtheorem{defin}{Definizione}
\newtheorem{oss}{Osservazione}
\newtheorem{ese}{Esempio}


\begin{document}
 $$\left(
\begin{array}{ccc}
x & y & 1 \\
\end{array}
\right)=\left(
\begin{array}{ccc}
x'& y' &1
\end{array}
\right)\left(
\begin{tabular}{ccc}
        & \multicolumn{2}{c}{$\gamma$}\\
\raisebox{1.5ex}[0cm][0cm]{$P$}
         &$\delta$                   \\
0\quad\,0&1                  \\
\end{tabular}
 \right)^t,$$
\end{document}
