Example

Example: Determining if a Sequence Is Arithmetic

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

5,9,13,17,21,25,5, 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.

4,9,12,17,20,25,4, 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.

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 2026-05-26

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Intermediate Algebra @ OpenStax

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

Algebra