If the second and fourth term of a G P are 8 an... - WAEC Mathematics 1989 Question
If the second and fourth term of a G.P are 8 and 32 respectively,what is the sum of the first four terms?
A
28
B
40
C
48
D
60
correct option: d
ar = 8 .....(1)
ar3 = 32 .....(2)
divide (2) by (1)
r2 = 4 r = 2 ∴ a = 4
S =
a(rn - 1)/r - 1
S =
4(24 - 1)/2 - 1 = 60
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