9. (i) If \( A =\left[\begin{array}{rr}2 & -1 \\ -1 & 2\end{array}\right] \), verify \( A ^{2}-4 A +3 I = O \), where \( I =\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right] \) and \( O =\left[\begin{array}{ll}0 & 0 \\ 0 & 0\end{array}\right] . \) Hence find \( A ^{-1} \)
(W. Bengal B. 2016 )
