Question

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Answer 1

5.

Calculăm determinantul :

$\left|\begin{array}{ccc}1&2&3\\0&1&2\\-1&2&1\end{array}\right| \stackrel{\ell_3+\ell_1}{=}\ \ \left|\begin{array}{ccc}1&2&3\\0&1&2\\0&4&4\end{array}\right| =4-8=-4\ne0 \Rightarrow rangA=3$