Find a closed form of $\sum=?iso-8859-1?Q?=5F{i=3D1}^n_i^3$_=96_math.stackexchange.com?=

Find a closed form of $\sum_{i=1}^n i^3$ – math.stackexchange.com

I'm trying to compute the general formula for $\sum_{i=1}^ni^3$. My math
instructor said that we should do this by starting with a grid of $n^2$
squares like so: $$ \begin{matrix} 1^2 & 2^2 …