Lim n->∞ 2n^2/(n^2+n+1) = Lim n->∞ 2n^2/(n^2+n+1) = Lim n->∞ 2n^2/n^2/(n^2/n^2+n/n^2+1/n^2) = 2/(1+0+0) = 2
делим на n^2
