\documentclass {article}

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\newtheorem{esercizio}{Esercizio}

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\author{Alcune soluzioni per gli esercizi 10/2/2010}
\title{Geometria e algebra lineare 2009/10}
\date{}
\begin{document}
\maketitle


\begin{esercizio}
$r = \big\{(2, -t+1, t)\ \big| \ t\in \matR\big\}$.

\end{esercizio}

\begin{esercizio}
\begin{enumerate}
\item $\big\{x+z = 2 \ \big|\ y=1\big\}$
\item $\big\{(t, 0, t-1)\ \big| \ t\in \matR\big\}$.
\end{enumerate}

\end{esercizio}

\begin{esercizio}
\begin{enumerate}

\item $\big\{x_1+x_2+x_3 = 1\big\}$.
\item
\item $\big\{ (1+t, 2-t+u, 3-u) \ \big| \ t,u\in\matR\big\}.$


\end{enumerate}
\end{esercizio}

\end{document}





