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Arithmetic

Series Formula

Example 1

Find the sum of the first 50 terms of an arithmetic sequence whose first term is -5 and whose 50th term is -95.

Step 1. Determine a1 and an.

SeriesFormulaEx1-1 and SeriesFormulaEx1-2

Step 2. Determine the number of pairs in the sequence.

SeriesFormulaEx1-3

Step 3. To find the series, substitute and solve.

SeriesFormulaEx1-4
SeriesFormulaEx1-5