Problems from Matrix concept and types of matrices

Development:

The element $a_{23}$ corresponds to row $2$ and column $3$, it is therefore $8$.

The element $a_{12}$ corresponds to row $1$ and column $2$, it is therefore $-13$.

Solution:

$a_{23}=8$ and $a_{12}=-13$.

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Development:

1. $\left(\begin{array}{cccc}2& 1& 5& 0\\ -3& 2& -1& 3\end{array}\right)$

2. $\left(\begin{array}{cc}2& 2\\ 0& 9\\ 0& 4\end{array}\right)$

Solution:

1. $\left(\begin{array}{cccc}2& 1& 5& 0\\ -3& 2& -1& 3\end{array}\right)$

2. $\left(\begin{array}{cc}2& 2\\ 0& 9\\ 0& 4\end{array}\right)$

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