$$\left. \begin{array} { l } { \quad x [ n ] = 8 [ n ] + 2 u [ n - 1 ] - 3 ^ { n } [ n - 2 ] } \end{array} \right.$$
$\left\{\begin{matrix}x=\frac{2\times 3^{n}}{n}-3^{n}+2u-\frac{2u}{n}+8\text{, }&n\neq 0\\x\in \mathrm{R}\text{, }&n=0\text{ and }u=1\end{matrix}\right.$
