19
次の和を求めよ。
(1) \(\displaystyle{\sum_{k=1}^{n}(3k^2-k)}\)
(2) \(\displaystyle{\sum_{k=1}^{n}(2k+1)(4k^2-2k+1)}\)
(3) \(\displaystyle{\sum_{k=11}^{20}(6k-1)}\)
(4) \(\displaystyle{\sum_{k=1}^{n+1}5^k}\)