Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=

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Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=Sn为等差数列{An}的前N

Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=
Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=

Sn为等差数列{An}的前N项和,若A2n/An=4n-1/2n-1,则S2n/Sn=
A2n /An=(4n-1)/(2n-1)代入:A2n=A1+(2n-1)d,An=A1+(n-1)d,可整理得:d=2A1,代入下式 S2n/Sn=[2nA1+2n*(2n-1)*d/2]/[nA1+n*(n-1)*d/2] =4

等差数列an的前n项和为sn 且s7=7 则a2+a6 设等差数列an,的前n项和为Sn,a2+a4=6,求S5 若等差数列{an}的前n项和为Sn,且a2+a3=6,则S4的值为等差数列｛An｝的前n项和为Sn,若A2=1,A3=3,则S4的值等差数列｛An｝的前n项和为Sn,若A2=1,A3=3,则S4的值设等差数列An的前n项和为Sn.若S9=72,a2+a4+a9=多少已知等差数列{an}的前n项和为Sn,若S12=21,求a2+a5+a8+a11 设等差数列{an}的前n项和为Sn,若S9= 72,则a2+a4+a9= 设等差数列{An}的前n项和为Sn,若A2+A8=15-A5,则S9等于? 已知等差数列｛An｝的前n项和为Sn,若 S12＝21,则A2+A5+A8+A11＝? 设等差数列｛An｝的前n项和为Sn,若S9＝72,则A2+A5+A9＝? 设等差数列an的前 n项和为Sn ,若S9=81 ,则a2+a5+a8=? 等差数列{an}的前n项和为Sn,若a2=1,a3=3,则S4等于等差数列{an}的前n项和为Sn,若a2+a6+a7=18,则S9=? 等差数列{an}的前n项和为Sn,若a2=1,a3=3,则S4等于等差数列{an}的前n项和为Sn,若a2=1,a3=3,则S4=? 等差数列an的前n项和为sn,若a2+a3=4,则s4= 设等差数列an的前n项和为Sn,若S7=49,a6=11,则a2=