$\therefore A B=B A$
$\left[\begin{array}{lll}0 & 1 & 0 \\ 1 & 0 & 0 \\ 0 & 0 & 1\end{array}\right]\left[\begin{array}{lll}a & b & c \\ d & e & f \\ g & h & i\end{array}\right]=\left[\begin{array}{lll}a & b & c \\ d & e & f \\ g & h & i\end{array}\right]\left[\begin{array}{lll}0 & 1 & 0 \\ 1 & 0 & 0 \\ 0 & 0 & 1\end{array}\right]$
$\left[\begin{array}{lll}d & e & f \\ a & b & c \\ g & h & i\end{array}\right]=\left[\begin{array}{lll}b & a & c \\ e & d & f \\ h & g & i\end{array}\right]$
$\Rightarrow d=b, e=a, f=c, g=h$
$\therefore$ Matrix $B=\left[\begin{array}{lll}a & b & c \\ b & a & c \\ g & g & i\end{array}\right]$
No. of ways of selecting $a, b, c, g$,
$\mathrm{i}=5 \times 5 \times 5 \times 5 \times 5$
$=5^{5}=3125$
$\therefore$ No. of Matrices $B=3125$
$x+y+z=2$
$x+2 y+3 z=5$
$x+3 y+\lambda z=\mu$
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