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# Could you show me the workings of this?

Mar 7, 2018

$a = - 15$

#### Explanation:

When adding matrices, simply add the elements in the same row and column of the terms to get the value of the element in the resulting sum matrix.

$\left(\begin{matrix}2 & - 5 \\ 4 & 1 \\ \textcolor{red}{- 2} & 2\end{matrix}\right) + \left(\begin{matrix}- 2 & 7 \\ - 7 & 2 \\ \textcolor{red}{- 8} & 2\end{matrix}\right) + \left(\begin{matrix}4 & - 4 \\ - 7 & - 6 \\ \textcolor{red}{- 5} & 4\end{matrix}\right)$

$\textcolor{w h i t e}{\text{XXX}} = \left(\begin{matrix}2 - 2 + 4 & - 5 + 7 - 4 \\ 4 - 7 - 7 & 1 + 2 - 6 \\ \textcolor{red}{- 2 - 8 - 5} & 2 + 2 + 4\end{matrix}\right)$

$\textcolor{w h i t e}{\text{XXX}} = \left(\begin{matrix}4 & - 2 \\ - 10 & - 3 \\ \textcolor{red}{- 15} & 8\end{matrix}\right)$