Sn等比，等差的公式。急

Question

如题所述

Answer 1

等差：Sn=n*a1+n(n-1)d/2或Sn=n(a1+an)/2
等比：Sn=a1(1-q^n)/(1-q) =(a1-an*q)/(1-q) (q≠1)
Sn=n*a1 (q=1)本回答被提问者和网友采纳

Answer 2

等差：Sn=(a1+an)n/2=a1n+n(n-1)d/2
等比：Sn=na1(q=1)
Sn=a1(1-q^n)/1-q (q不等于1）

Answer 3

等差数列
Sn=(2a1+dn-n)n/2
等比数列
Sn=a1*(1-q^n)/(1-q)

Answer 4