Question

一道高一数学题！急！在线等！要有具体过程！

数列{an}中，a3=2,a7=1,且数列{1/（an+1)}是等差数列，则a8=？

Answer 1

1/(a5+1)=1/2(1/(a3+1)+1/(a7+1))=5/12

1/(a7+1)=1/2(1/(a3+1)+1/(a11+1))
1/2=1/2(1/3+)1/(a11+1)
1/(a11+1)=-1/3

1/(a8+1)=1/2(1/(a5+1)+1/(a11+1))=1/2(5/12-1/3)=1/24
a8=23