WAEC - Mathematics (1990 - No. 13)
Find the sum of the first five terms of the G.P 2,6, 18 ....
484
243
242
130
121
Explanation
\(S_{n} = \frac{a(r^n - 1)}{r - 1}\)
a = 2; r = 6/2 = 3.
\(S_{5} = \frac{2(3^5 - 1)}{3 - 1}\)
= \(243 - 1 = 242\)
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