等差数列{An}前n项和为Sn,a2+a6=8,则S7=?
1个回答
a1+a7=a2+a6=a3+a5=2a4=8
∴ S7=(a1+a7)+(a2+a6)+(a3+a5)+a4=8+8+8+4=28
相关问题
已知等差数列{an}的前n项和为Sn,若2a6=a8+6,则S7是( )
设等差数列an的前n项和为Sn,若S7=49,a6=11,则a2=
设Sn为等差数列(An)的前n项和,S8=4A3,A7=-2,则A9=?
等差数列an中,前n项和为Sn,且S6S8,则:
设等差数列{an}的前n项和为Sn,若S3=9,S6=36,则a7+a8+a9=______.
设等差数列{an}的前n项和为Sn,若S3=9,S6=36,则a7+a8+a9=______.
设等差数列{an}的前n项和为Sn,若S3=9,S6=36,则a7+a8+a9=______.
设等差数列{an}的前n项和为Sn,若S3=9,S6=36,则a7+a8+a9=______.
等差数列{an}的前n项和为Sn,若a3+a7+a11=6,则S13=______.
sn为等差数列{an}的前n项和,s2=s6,a4=1则a5=