Question on: JAMB Mathematics - 1999
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
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Correct Option: C
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
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
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