# Problems from Matrix concept and types of matrices

What values do the elements $$a_{23}$$ and $$a_{12}$$ have in the matrix $$\left(\begin{array}{ccc} 42 & -13 & 0 \\ 31 & 12 & 8 \end{array} \right)$$

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### 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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Use the Formula editor to represent:

1. a matrix with two rows and four columns.
2. a $$3\times2$$ matrix.
See development and solution

### 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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