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Which of the following is(are) $NOT$ the square of a $3 \times 3$ matrix with real entries ?
$[A]$ $\left[\begin{array}{ccc}1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & -1\end{array}\right]$
$[B]$ $\left[\begin{array}{ccc}-1 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & -1\end{array}\right]$
$[C]$ $\left[\begin{array}{lll}1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1\end{array}\right]$
$[D]$ $\left[\begin{array}{ccc}1 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & -1\end{array}\right]$
$A,B$
$A,C$
$A,D$
$A,B,C$
Solution
$|\mathrm{A}|^2$ cannot be $-\mathrm{ve}$
$\Rightarrow A$ and $B$ option cannot be square of matrix
$C$ option is $\left|\begin{array}{lll}1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1\end{array}\right|^2$
$D$ option is $\left|\begin{array}{ccc}1 & 0 & 0 \\ 0 & 0 & 1 \\ 0 & -1 & 0\end{array}\right|^2$