A geometric sequence has first term 2 and common ratio 3. Find the sum of its first 6 terms.
Answer and explanation
Correct answer: B. 728
- Step 1: Use S_n = a(r^n - 1)/(r - 1) for r not equal to 1.
- Step 2: S = 2(3^6 - 1)/(3 - 1) = 2 x 728 / 2 = 728.
Answer
728.
Why not the others: '486' gives the last term instead of the sum; '1458' gives the (n+1)th term; '730' adds the first term twice.
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