$A=\left[\begin{array}{ll}1 & 2 \\\\ 2 & 1\end{array}\right]$ and $B=\left[\begin{array}{ll}x & y \\\\ 1 & 2\end{array}\right]$ are two matrices such that $(A+B)(A-B)=A^{2}-B^{2}$ If $C=\left[\begin{array}{ll}x & 2 \\\\ 1 & y\end{array}\right]$, then trace $(C)=$

If $x=k$ satisfies the equation $\left|\begin{array}{ccc}x-2 & 3 x-3 & 5 x-5 \\\\ x-4 & 3 x-9 & 5 x-25 \\\\ x-8 & 3 x-27 & 5 x-125\end{array}\right|=0$, then $x=k$ also satisfies the equation

If $A$ is a non-singular matrix, then $\operatorname{adj}\left(A^{-1}\right)=$