Question:
Find matrix $A$, if $\left[\begin{array}{rrr}1 & 2 & -1 \\ 0 & 4 & 9\end{array}\right]+A=\left[\begin{array}{rrr}9 & -1 & 4 \\ -2 & 1 & 3\end{array}\right]$
Solution:
Here,
$A=\left[\begin{array}{ccc}9 & -1 & 4 \\ -2 & 1 & 3\end{array}\right]-\left[\begin{array}{ccc}1 & 2 & -1 \\ 0 & 4 & 9\end{array}\right]$
$\Rightarrow A=\left[\begin{array}{ccc}9-1 & -1-2 & 4+1 \\ -2-0 & 1-4 & 3-9\end{array}\right]$
$\Rightarrow A=\left[\begin{array}{ccc}8 & -3 & 5 \\ -2 & -3 & -6\end{array}\right]$