MCQ
If $A=\left[\begin{array}{ccc}1 & -1 & 0 \\ 2 & 3 & 4 \\ 0 & 1 & 2\end{array}\right]$ and $B=\left[\begin{array}{ccc}2 & 2 & -4 \\ -4 & 2 & -4 \\ 2 & -1 & 5\end{array}\right]$, then
  • A
    $A^{-1}=B$
  • B
    $A^{-1}=6 B$
  • C
    $B^{-1}=B$
  • $B^{-1}=\frac{1}{6} A$

Answer

Correct option: D.
$B^{-1}=\frac{1}{6} A$
We have,
$\begin{array}{l} A B=\left[\begin{array}{ccc} 1 & -1 & 0 \\ 2 & 3 & 4 \\ 0 & 1 & 2 \end{array}\right]\left[\begin{array}{ccc} 2 & 2 & -4 \\
-4 & 2 & -4 \\ 2 & -1 & 5 \end{array}\right] \end{array} $
$ =\left[\begin{array}{ccc} 2+4+0 & 2-2+0 & -4+4+0 \\ 4-12+8 & 4+6-4 & -8-12+20 \\
0-4+4 & 0+2-2 & 0-4+10 \end{array}\right]  $
$ =\left[\begin{array}{lll} 6 & 0 & 0 \\ 0 & 6 & 0 \\ 0 & 0 & 6 \end{array}\right] $
$=61 $
$\Rightarrow B^{-1}=\frac{1}{6} A$

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