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Effectuer le produit des matrices : \[\left( \begin{array}{cc} 2 & 1 \\ 3& 2 \end{array} \right)\times \left( \begin{array}{cc}1 & -1 \\ 1& 2 \end{array} \right) \ \ \ \ \left( \begin{array} {ccc} 1 & 2 & 0 \\ 3 & 1 & 4 \end{array} \right) \times \left( \begin{array}{ccc} -1 &-1& 0 \\ 1 & 4 & -1 \\ 2 & 1 & 2\end{array} \right) \ \ \ \ \left( \begin{array}{ccc} a &b& c \\ c & b & a \\ 1 & 1 & 1\end{array} \right) \times \left( \begin{array}{ccc} 1 &a& c \\ 1 & b & b \\ 1 & c & a\end{array} \right)\]