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Definition

Geometric Sequence

A geometric sequence is a sequence in which the ratio between every pair of consecutive terms is always the same constant value. Unlike an arithmetic sequence, where each term is obtained by adding a fixed amount, each term in a geometric sequence is obtained by multiplying the previous term by this fixed constant. Using subscript notation, a sequence a1,a2,a3,a_1, a_2, a_3, \dots is geometric when anan1\frac{a_n}{a_{n-1}} produces the same number for every integer n2n \geq 2. For example, 4,8,16,32,64,128,4, 8, 16, 32, 64, 128, \dots is a geometric sequence because each term is exactly 22 times the previous term, while a sequence like 2,6,12,36,72,216,-2, 6, -12, 36, -72, 216, \dots is not geometric because the ratios between consecutive terms alternate between 3-3 and 2-2.

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Updated 2026-05-25

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

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