Example

Examples: Determining if a Sequence Is Arithmetic and Finding the Common Difference

Determine whether each sequence is arithmetic and, if so, state the common difference.

  1. 5, 9, 13, 17, 21, 25, dots Subtract consecutive terms: 95=49 - 5 = 4, 139=413 - 9 = 4, 1713=417 - 13 = 4, 2117=421 - 17 = 4, 2521=425 - 21 = 4. Every difference equals 44, so the sequence is arithmetic with d=4d = 4.

  2. 4, 9, 12, 17, 20, 25, dots Subtract consecutive terms: 94=59 - 4 = 5, 129=312 - 9 = 3, 1712=517 - 12 = 5, 2017=320 - 17 = 3, 2520=525 - 20 = 5. The differences alternate between 55 and 33, so the sequence is not arithmetic and has no common difference.

  3. 10,3,4,11,18,25,10, 3, -4, -11, -18, -25, \dots Subtract consecutive terms: 310=73 - 10 = -7, 43=7-4 - 3 = -7, 11(4)=7-11 - (-4) = -7, 18(11)=7-18 - (-11) = -7, 25(18)=7-25 - (-18) = -7. Every difference equals 7-7, so the sequence is arithmetic with d=7d = -7.

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Updated 2026-06-30

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Intermediate Algebra @ OpenStax

Ch.12 Sequences, Series and Binomial Theorem - Intermediate Algebra @ OpenStax

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