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Să se calculeze [tex]f(A)[/tex] dacă : a) [tex]A=\left([tex]\begin{array}{rr}1 & -1 \\ 2 & 1\end{array}\right), f(X)=X^{2}-5 X+7 I_{2}[/tex];

b) [tex]A=\left(\begin{array}{rrr}1 & -1 & 1 \\ 2 & 0 & -2 \\ 3 & 3 & 3\end{array}\right), f(X)=3 X^{2}-7 X-4 I_{3}[/tex][/tex]