MCQ
If $P = \left( {\begin{array}{*{20}{c}}i&0&{ - i}\\0&{ - i}&i\\{ - i}&i&0\end{array}} \right)$ and $Q = \left( {\begin{array}{*{20}{c}}{ - i}&i\\0&0\\i&{ - i}\end{array}} \right)$,then $PQ$ is equal to
  • A
    $\left( {\begin{array}{*{20}{c}}{ - 2}&2\\1&{ - 1}\\1&{ - 1}\end{array}} \right)$
  • $\left( {\begin{array}{*{20}{c}}{\,2}&{ - 2}\\{ - 1}&{\,\,\,1}\\{ - 1}&{\,\,\,1}\end{array}} \right)$
  • C
    $\left( {\begin{array}{*{20}{c}}2&{ - 2}\\{ - 1}&{\,\,1}\end{array}} \right)$
  • D
    $\left( {\begin{array}{*{20}{c}}1&0&0\\0&1&0\\0&0&1\end{array}} \right)$

Answer

Correct option: B.
$\left( {\begin{array}{*{20}{c}}{\,2}&{ - 2}\\{ - 1}&{\,\,\,1}\\{ - 1}&{\,\,\,1}\end{array}} \right)$
b
(b) First note that $PQ$ must be of order $3 × 2$ and its $(1, 1)$th entry is $i( - i) + 0 - i(i) = 2$.

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