Back to Derive geometric series formula — Problem 3 · Task Set 8

Exercises: Geometric Series Formula

For each problem, identify the parameters a, r, and n before applying any formula. Always check whether r = 1. Show your work for computation problems.

Grade 9·22 problems·~45 min·Common Core Math - HS Algebra·standard·hsa-sse-b-4

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Recall / Warm-Up

What is the difference between the 5th term and the sum of the first 5 terms of the sequence $2, 6, 18, 54, 162$ ?

There is no difference — the 5th term equals the sum.

The 5th term is 162; the sum of the first 5 terms is $2 + 6 + 18 + 54 + 162 = 242$ .

The 5th term is 242 (the accumulated sum).

The sum of 5 terms equals $a \cdot r^5 = 2 \cdot 3^5 = 486$ .