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Calculer l’inverse de : \[\left( \begin{array}{llll} 1 & ... & ... & 1 \\ 0 & 1 & ... & ... \\ ... & 0 & 1 & ... \\ 0 & ... & 0 & 1 \end{array} \right) ,\left( \begin{array}{llll} 1 & 2 & ... & n \\ 0 & 1 & 2 & ... \\ ... & 0 & 1 & 2 \\ 0 & ... & 0 & 1 \end{array} \right) .\]