MCQ
If $A=\left[\begin{array}{ll}2 & 3 \\ 4 & 2\end{array}\right]$ and $B=\left[\begin{array}{ll}1 & 2 \\ 3 & 4\end{array}\right]$, then the matrix $B A$ is:
  • A
    $\left[\begin{array}{ll}11 & 16 \\ 10 & 16\end{array}\right]$
  • B
    $\left[\begin{array}{rr}10 & 22 \\ 7 & 17\end{array}\right]$
  • C
    $\left[\begin{array}{ll}11 & 10 \\ 16 & 16\end{array}\right]$
  • $\left[\begin{array}{rr}10 & 7 \\ 22 & 17\end{array}\right]$

Answer

Correct option: D.
$\left[\begin{array}{rr}10 & 7 \\ 22 & 17\end{array}\right]$
(d) $\left[\begin{array}{cc}10 & 7 \\ 22 & 17\end{array}\right]$
Explanation:
$\begin{array}{l} BA =\left[\begin{array}{ll}1 & 2 \\ 3 & 4\end{array}\right]\left[\begin{array}{ll}2 & 3 \\ 4 & 2\end{array}\right] \\ =\left[\begin{array}{ll}1 \times 2+2 \times 4 & 1 \times 3+2 \times 2 \\ 3 \times 2+4 \times 4 & 3 \times 3+4 \times 2\end{array}\right] \\ =\left[\begin{array}{cc}10 & 7 \\ 22 & 17\end{array}\right]\end{array}$

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