设Sn是等差数列{an}的前n项和,若S7=35,则a4=_.

问题描述:

设Sn是等差数列{an}的前n项和,若S7=35,则a4=______.

S7=

(a1+a7)•7
2
=35,
∴a1+a7=10
∴2a4=a1+a7=10,a4=5
故答案为5.