设Sn是等差数列an的前n项和,已知a2=3,S11=121,则S7等于
设Sn是等差数列an的前n项和,已知a2=3,S11=121,则S7等于
设Sn是等差数列{an}的前n项和,已知a2=3,S11=121,则S7=
设Sn是等差数列{an}的前n项和,已知a1=3,a2=11,则S7等于?
Sn是等差数列{an}的前n项和,已知a2=3,a6=11则S7等于几
设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7等于( )
设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7=______.
设sn为等差数列an的前n项和已知a1+a2+a6=15 s7大于等于49 1.求...
设Sn是等差数列{an}的前n项和,S7=3(a2+a12),则a7a4的值为( )
设Sn为等差数列{an}的前n项和,S7=42,Sn=510,若a(n-3)=45(n>7),则n等于
sn为等差数列an的前n项和 已知S3/S7=2/5 则a2/a4
已知等差数列{an}的前n项和为Sn,且a2=1,S11=33.
已知Sn为等差数列{an}的前n项和,若a2:a4=7:6,则S7:S3等于______.