一道数列题4已知数列{an}中,a1=2,a4=1,且数列{1/an}为等差数列,求a10感激不尽了.

Question

一道数列题4
已知数列{an}中,a1=2,a4=1,且数列{1/an}为等差数列,求a10
感激不尽了.

Answer 1

1/a1 = 1/2
1/a4 = 1
1/a4 = 1/a1 + 3d
d = 1/6
1/a10 = 1/a1 + 9d = 1/2 + 9 × (1/6) = 2
a10 = 1/2