$-4a-3$

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

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

$a+3$

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

$3,3$

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