\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Solve by Gauss the \(3 \times 3\) system \(\{x + y - z = 0 \;;\; 2 x - y + z = 3 \;;\; x + 2 y + z = 7\}\).
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