Question
If A = $\left[\begin{array}{lll} {3} & {\sqrt{3}} & {2} \\ {4} & {2} & {0} \end{array}\right] \text { and } B=\left[\begin{array}{rrr} {2} & {-1} & {2} \\ {1} & {2} & {4} \end{array}\right]$ verify that
  1. (A′)′ = A
  2. (A + B)′ = A′ + B′
  3. (kB)′ = kB′, where k is any constant.

Answer

  1. We have
    A = $\left[\begin{array}{lll} {3} & {\sqrt{3}} & {2} \\ {4} & {2} & {0} \end{array}\right] $
    $\Rightarrow \mathrm{A}^{\prime}=\left[\begin{array}{cc} {3} & {4} \\ {\sqrt{3}} & {2} \\ {2} & {0} \end{array}\right] $
    $\Rightarrow$ (A')' = $\left[\begin{array}{ccc} {3} & {\sqrt{3}} & {2} \\ {4} & {2} & {0} \end{array}\right]$ = A
    Thus (A′)′ = A
  2. We have
    A = $\left[\begin{array}{lll} {3} & {\sqrt{3}} & {2} \\ {4} & {2} & {0} \end{array}\right], B=\left[\begin{array}{rrr} {2} & {-1} & {2} \\ {1} & {2} & {4} \end{array}\right] \Rightarrow A+B=\left[\begin{array}{rrr} {5} & {\sqrt{3}-1} & {4} \\ {5} & {4} & {4} \end{array}\right]$
    Therefore (A + B)' = $\left[\begin{array}{ccc} {5} & {5} \\ {\sqrt{3}} {-1} & {4} \\ {4} & {4} \end{array}\right]$
    Now A' = $\left[\begin{array}{cc} {3} & {4} \\ {\sqrt{3}} & {2} \\ {2} & {0} \end{array}\right], B^{\prime}=\left[\begin{array}{cc} {2} & {1} \\ {-1} & {2} \\ {2} & {4} \end{array}\right]$
    So A' + B' = $\left[\begin{array}{ccc} {5} & {5} \\ {\sqrt{3}} {-1} & {4} \\ {4} & {4} \end{array}\right]$
    Thus (A + B)′ = A′ + B′
  3. We have,
    $kB$ = k$\left[\begin{array}{rrr} {2} & {-1} & {2} \\ {1} & {2} & {4} \end{array}\right]=\left[\begin{array}{ccc} {2 k} & {-k} & {2 k} \\ {k} & {2 k} & {4 k} \end{array}\right]$
    $\therefore$ $(kB)'$ = $\left[\begin{array}{cc} {2 k} & {k} \\ {-k} & {2 k} \\ {2 k} & {4 k} \end{array}\right]=k\left[\begin{array}{cc} {2} & {1} \\ {-1} & {2} \\ {2} & {4} \end{array}\right]=k \mathrm{B}^{\prime}$
    Thus $(kB)' = kB'$

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