How to Find Partial Sums for Geometric Sequences
- 1). Write the geometric sequence you want to analyze. For example, you write, "3, 9, 27, 81, 243."
- 2). Divide the second term by the first term and write your answer as R. For example, 9/3 = 3. You write, "R = 3."
- 3). Count the number of terms you want to sum and write the number as N. For example, you are summing five terms. You write, "N = 5."
- 4). Find the difference of 1 and R to the Nth power using a calculator. For example, 1 - 3^5 = -242.
- 5). Divide your answer by the difference of 1 and R. For example, -242/(1 - 3) = 121.
- 6). Multiply your answer by the first term in your series. For example, the first term in your series is 3: 3 x 121 = 363. The partial sum of your geometric series is 363.
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