因为数列{1/an+1}是等差数列,设其公差为d,则
1/(a3 +1) + 4d = 1/(a7 +1)
可求得 d = 1/24
故 1/(a8 +1) = 1/(a7 +1) + d = 1/2 +1/24 = 13/24
a8 = 24/13 -1 = 11/13
因为数列{1/an+1}是等差数列,设其公差为d,则
1/(a3 +1) + 4d = 1/(a7 +1)
可求得 d = 1/24
故 1/(a8 +1) = 1/(a7 +1) + d = 1/2 +1/24 = 13/24
a8 = 24/13 -1 = 11/13