等差数列前n项和Sn,S4=2,S8=6,则S20=

等差数列前n项和Sn,S4=2,S8=6,则S20= 已知等差数列an的前n项和为Sn,S4/S8=1/2,那么S8/S12=? sn为等差数列an的前n项和,S8-S4=12,则S12 设等差数列{an}的前n项和Sn,且S4/S8=1/3,则S8/S16=? 已知等差数列{an}中的前n项和为Sn,且S4/S8=1/3,那么S8/S16等于? 设Sn是等差数列an的前n项和,s4/s12=1/6 则s8/s16=? 若{an}是个等差数列,前n项和为sn,已知S4=6 S8=20 求S12 已知等差数列an 的前n项和为sn ,s4=6,s12=18 求s8 等比数列｛an｝前n项和为Sn,S4=2,S8=6,求S12. 设Sn为等差数列{an}的前n项和,S4=14,S20-S8=30,则S8=设Sn为等差数列{an}的前n项和,S4=14,S20-S7=30,则S8= 等差数列{an}中,Sn为其前n项和,若S4=1,S8=4,S20-S16=?等差数列{an}中,Sn为其前n项和,若S4=1,S8=4,S20-S16=? 设Sn是等差数列{an}的前n和,若S4/S8=1/3则S8/S16=? 设等差数列{an}的前n项和为Sn,且S4=20,S8=72,则S12=? 已知等差数列{an},前n项和为Sn,若S4=8,S8=4,求S12 若Sn为等差数列前n项和,且S8-S4=12,则S12的值为? 设等比数列{an}前n项和为Sn,若S8:S4=2:3,则S12:S4=?9 已知等差数列{an}的前n项和为Sn,且S4/S8=1/3,则S8/S16等于_ 设Sn是等差数列｛an｝的前n项和,若S8/S4 =3,则S16/S8等于多少,为什么