A geometric sequence has first term 2 and common ratio 3. What is the sum of its first 4 terms?
Answer and explanation
Correct answer: C. 80
- Step 1: S_n = a_1 (q^n - 1) / (q - 1).
- Step 2: S_4 = 2 x (3^4 - 1) / 2 = 80.
Answer
80.
Why not the others: The other values use one term too many, give a single term, or forget to divide by q - 1.
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