设Sn是等差数列前n项和,已知a1=3,a7=11,则S7=
设Sn是等差数列前n项和,已知a1=3,a7=11,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?
来达人~~数列Sn是等差数列An的前n项和 ~~若A7/A4=2则 S13/S7=?2.等差数列An中 A1+A4+A1
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a2=3,S11=121,则S7等于
设Sn是等差数列{an}的前n项和,已知3a4=7a7,且a1>0,当Sn取最大值时,求n!
已知等差数列的前n项和为Sn,a3-a8=13,且S7=35,则a7
设Sn是等差数列{an}的前n项和,已知a2=3,a6=11,则S7=______.
设Sn是等差数列{an}的前n项和,已知a2=3,a6=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
设等差数列{an}的前n项和为Sn,若a1=-11,a3+a7=-6,则当Sn取最小值时,n等于( )
已知等差数列{an}中,a1=11,前7项的和S7=35,则前n项和Sn中( )