1、在等差数列{an}中,a1+a2=3,a3+a4=6,a7+a8的值求
问题描述:
1、在等差数列{an}中,a1+a2=3,a3+a4=6,a7+a8的值求
答
12,S2,S4-S2,S6-S4,S8-S6成等差数列
答
12lS2517S4-S2,S6-S4,S8-S6成等差数列
答
1273S2,S4-S2S6-S4,S8-S6成等差数列
答
a3+a4=(a1+a2)+4d
d=3/4
(a7+a8)=(a1+a2)+12d=(a3+a4)+8d
=12
答
∵ a3 + a4 = (a1 + 2d)+ (a2 + 2d) = a1 + a2 + 4d ∴ (a3 + a4)-(a1 + a2) = (a1 + a2 + 4d)-(a1 + a2) = 6 - 3 = 3 = 4d ∴ d = 3 /...