Sum of the first 8 terms of 2, 6, 18, 54, …
Use the partial-sum formula for a geometric sequence with ratio 3.
Solution
- Given a₁ = 2, common ratio r = 3, n = 8
- nth term aₙ = a₁·r^(n−1) = 2·3^7 = 4374
- Sum of n terms Sₙ = a₁·(1 − rⁿ)/(1 − r) = 6560
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