MCQ
If $A=\left[\begin{array}{ll}3 & 9 \\ 7 & 2\end{array}\right]$ and $I$ is an identity matrix of order 2 , then the value of $A+5 I$ is:
  • A
    $\left[\begin{array}{cc}3 & 14 \\ 12 & 2\end{array}\right]$
  • B
    $\left[\begin{array}{ll}3 & 9 \\ 7 & 2\end{array}\right]$
  • $\left[\begin{array}{ll}8 & 9 \\ 7 & 7\end{array}\right]$
  • D
    $\left[\begin{array}{cc}8 & 14 \\ 12 & 7\end{array}\right]$

Answer

Correct option: C.
$\left[\begin{array}{ll}8 & 9 \\ 7 & 7\end{array}\right]$
(c)$\left[\begin{array}{ll}8 & 9 \\ 7 & 7\end{array}\right]$
Explanation:
$\begin{array}{l}A+5 I=\left[\begin{array}{ll}3 & 9 \\ 7 & 2\end{array}\right]+5\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right] \\ =\left[\begin{array}{ll}3 & 9 \\ 7 & 2\end{array}\right]+\left[\begin{array}{ll}5 & 0 \\ 0 & 5\end{array}\right]=\left[\begin{array}{ll}8 & 9 \\ 7 & 7\end{array}\right]\end{array}$

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