given sigma from $i=1$ to $n$ of $(1-(i^2/n)^2)(1/n))$
how would you factor this function to isolate $i^2$ and get $[n(n+1)(2n+1)]/6$ ?
update... I got until the limit as n approaches infinity (1/n) sigma from i=1 to n (1-(i^2/n^2))
I still am unable to factor out (1-(i^2/n^2)) outside the sigma and just leave i^2 inside the sigma function.