Question
Construct a $2 \times 2$ matrix $A = [a_{ij}]$ whose element $a_{ij} $ is given by: $\frac{(i+j)^{2}}{2}$

Answer

Let $A = [a_{ij}]_{2\times2}$
So, the elements in a $2\times2$ matrix are
$a_{11}, a_{12}, a_{21}, a_{22},$
$A =  \begin{bmatrix}a_{11}&a_{12}\\a_{21}&a_{22}\end{bmatrix} ...(i)$
$a_{11} =\frac{\left(1+1\right)^2}2 = \frac42 = 2$
$a_{12} = \frac{(1+2)^{2}}{2}=\frac{3^{2}}{2}=\frac{9}{2} $
$a_{21} = \frac{(2+1)^{2}}{2}=\frac{3^{2}}{2}=\frac{9}{2}$
$a_{22} = \frac{(2+2)^{2}}{2}=\frac{4^{2}}{2}=\frac{16}{2} = 8$
So, $(i)$ becomes
$A = \left(\begin{array}{cc} {2} & {\frac 92} \\ {\frac92} & {8} \end{array}\right)$

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