$-13$

$\left(\begin{matrix}1&1&-1\\3&-1&2\\1&2&1\end{matrix}\right)$

$\left(\begin{matrix}\frac{5}{13}&\frac{3}{13}&-\frac{1}{13}\\\frac{1}{13}&-\frac{2}{13}&\frac{5}{13}\\-\frac{7}{13}&\frac{1}{13}&\frac{4}{13}\end{matrix}\right)$

$1$

$\left(\begin{matrix}1&3&1\\1&-1&2\\-1&2&1\end{matrix}\right)$

$3,3$

$\left(\begin{matrix}1&0&0\\0&1&0\\0&0&1\end{matrix}\right)$

$\left[\begin{array}{rrr}-5 & -3 & 1 \\ -1 & 2 & -5 \\ 7 & -1 & -4\end{array}\right]$