alleryFor a GP with first a, ratio r≠1 and positive integer n, Sₙ equals
Aa(1−r)/(1−rⁿ)
Ba(1−rⁿ⁻¹)/(1−r)
Ca(1−rⁿ)/(1−r)
Dar(1−rⁿ)/(1−r)
Answer & Solution
Correct answer: C. a(1−rⁿ)/(1−r)
The first n powers from r⁰ to rⁿ⁻¹ sum to (1−rⁿ)/(1−r), multiplied by a.
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