等差数列{an}中,已知a3+a15=40,则S17=_.

问题描述:

等差数列{an}中,已知a3+a15=40,则S17=______.

S17=

17(a1+a17)
2
=
17(a3+a15)
2
=
17×40
2
=340
故答案为:340