This is LaTeX code:

[latex]
${\displaystyle\frac{1+2^3+...+n^3}{n^4}=\frac{{\left(\frac{n\cdot\left(n+1\rigjt)}{2}}\right)^2}{n^4}}=\frac{{n^2\cdot\left(n+1\rigjt)}^2}{4\cdot n^4}}$
[/latex]