The first term of a geometric progression is twice its common ratio. Find the sum of the first two terms of the G.P if its sum to infinity is 8.
-
A.
8/5 -
B.
8/3 -
C.
72/25 -
D.
56/9
Correct Answer: Option C
Explanation
Le the common ratio be r so that the first term is 2r.
Sum, s = a/(1-r)
ie. 8 = 2r/(1-r)
8(1-r) = 2r, r = 8/5.
Sn = a(1-rn)/(1-r)
Solve further to get 72/25