matrix

 

${\left[\frac{\mathrm{k}(\mathrm{k}+1)}{2}\right]}^2$

${\mathrm{ }}^{}$

$\frac{4n^2(2n+1{)}^2}{4}-\frac{8{\left[n^2(n+1)\right]}^2}{4}$

${\mathrm{ }}^{}$

${\left[\frac{\mathrm{2n}(\mathrm{2n}+1)}{2}\right]}^2$-8${\left[\frac{\mathrm{n}(\mathrm{n}+1)}{2}\right]}^2$

${\mathrm{ }}^{}$

$\left(\begin{array}{ccc}1& 2& 2\\ 2& 2& 2\\ 2& 2& 2\end{array}\right)$

$$

$$

$$

$$

${\left[\frac{\mathrm{s}(s+1)}{2}\right]}^2$

${\left[\frac{\mathrm{k}(\mathrm{k}+1)}{2}\right]}^2$

$$