Question:
Find matrix $X$, if $\left[\begin{array}{rrr}3 & 5 & -9 \\ -1 & 4 & -7\end{array}\right]+X=\left[\begin{array}{lll}6 & 2 & 3 \\ 4 & 8 & 6\end{array}\right]$.
Solution:
Given $\left[\begin{array}{ccc}3 & 5 & -9 \\ -1 & 4 & -7\end{array}\right]+x=\left[\begin{array}{lll}6 & 2 & 3 \\ 4 & 8 & 6\end{array}\right]$
$x=\left[\begin{array}{lll}6 & 2 & 3 \\ 4 & 8 & 6\end{array}\right]-\left[\begin{array}{ccc}3 & 5 & -9 \\ -1 & 4 & -7\end{array}\right]$
$=\left[\begin{array}{ccc}3 & -3 & 12 \\ 5 & 4 & 13\end{array}\right]$
Conclusion : $x=\left[\begin{array}{ccc}3 & -3 & 12 \\ 5 & 4 & 13\end{array}\right]$