已知等差数列前n项和为Sn=2n^2+an,a为常数,则公差d=

分类: 作业答案 • 2022-03-21 12:51:52

问题描述：

答

(1)Sn=n*a1+n*(n-1)*d
=n^2*d/2+n*a1-n*d/2
=d/2*n^2+(a1-d/2)*n/2
(2)d/2=2,
(3) d=4