设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n?

设Sn是等差数列an的前n项和,a5=2,an-4=30(n≥5,n∈N*),Sn=136,求n 设Sn是等差数列an的前n项和a5=2,an-4=30Sn=136,n>=5求n? 设sn是等差数列{an}的前n项和, 若a5：a7=2：3,求s9:(s13-s9) 设Sn是等差数列an的前n项和,a5=2,an-4=30,Sn=136求n! 设Sn是等差数列 an 的前n项和,S7=3(a3+a7),求a5/a4的值 设sn是等差数列an的前n项和,S5=3(a2+a8),则a5/a3的值 设Sn是等差数列an的前n项和,a5=5a3,则S9/S5=? 设Sn是等差数列an的前n项和,若a5/a3=5/9,则S9/S5= 设sn是等差数列{an}的前n项和,若s9/s5=9/5,则a5/a3= 设sn是等差数列an的前n项和,若a6/a5=9/11,则S11/S9 等差数列一道题{an}{bn}是等差数列前n项的和分别是Sn和Tn sn/tn =7n+2/n+3 求a5/b5 设等差数列{an},{bn}的前n项和分别是Sn,Tn,且Sn/Tn=7n+2/n+3求a5/b5 已知{an}是等差数列,记bn=anan+1an+2(n∈N*),设Sn为{bn}的前n项和,且3a5=8a12＞0,则当Sn取最大值时,n= 设Sn为等差数列{An}的前n项和,求证：{Sn/n}是等差数列 设等差数列{An}的前n项和为Sn,若A5=5A3,则S9/S5=? 设等差数列{an}的前n项和为Sn,若a5=5a3,则S9/S5=? 设等差数列｛AN｝的前N项和为SN,若A5=5A3则S9/S5=?. 设等差数列an的前 n项和为Sn ,若S9=81 ,则a2+a5+a8=?