若等差数列{an}满足a2+S3=8,a4+S7=16,则a3的值是

题目

若等差数列{an}满足a2+S3=8,a4+S7=16,则a3的值是

答案

等差数列中有
S(2n-1) = (2n-1)an
所以8 = a2 + S3 = 4a2
a2 = 2
同理a4 = 2
所以a3 = 2