Math 2.0

Sequences, series, summability Definition

Geometric sequence

Builds on Real sequence

Definition

Let aa and rr be real numbers. The geometric sequence with initial term aa and common ratio rr is the real sequence (a rn)n∈ℕ(a\,r^n)_{n \in \mathbb{N}}. Its terms are a,ar,ar2,ar3,…a, a r, a r^2, a r^3, \dots, and each term is rr times the term before it.

Remarks

Many texts require a≠0a \ne 0 and r≠0r \ne 0, so that the quotient of two consecutive terms is always rr. The sequence 1,2,4,8,…1, 2, 4, 8, \dots has a=1a = 1 and r=2r = 2. The sequence 1,1/2,1/4,…1, 1/2, 1/4, \dots has r=1/2r = 1/2. For ∣r∣<1|r| < 1, the sequence converges to 00. For r>1r > 1 and a>0a > 0, it tends to infinity. The sum of the terms is the geometric series.

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  1. Sequence definition
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114 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Geometric_progression, lead section
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MSC40A05
DefinesGeometric sequence
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