S2n,公差是多少?
假设等差数列{An}公差为d,则Sn,S2n-Sn,S3n-S2n,.....公差是多少?假设等差数列{An}公差为d,则Sn,S2n-Sn,S3n-S2n,.....公差是多少?
公差是(n^2)d 没错,你自己是对的,不用怀疑!!!
S2n-Sn=a(n+1)+a(n+2)+....+a(2n) Sn=a1+a2+a3+....+an 两个式子相减 (S2n-Sn)-Sn=nd 所以 则Sn,S2n-Sn,S3n-S2n,.....公差是nd
答:Sn,S2n-Sn,S3n-S2n成公差为n²d的等差数列推导: Sn=a1+a2+......+an S2n-Sn=a(n+1)+a(n+1)+.....详情>>
答:应该完全没区别。详情>>