Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025
Definition
An infinite geometric sequence is a sequence of numbers where each term after the first is found by multiplying the previous term by a fixed, non-zero number called the common ratio. The sequence continues indefinitely without terminating.
The general form of an infinite geometric sequence is $a, ar, ar^2, ar^3, \ldots$, where $a$ is the first term and $r$ is the common ratio.
If the absolute value of the common ratio $|r| < 1$, the infinite geometric series converges to a sum.
The sum of an infinite geometric series with $|r| < 1$ can be calculated using the formula $S = \frac{a}{1 - r}$.
If $|r| \geq 1$, the infinite geometric series does not converge and thus has no sum.
Infinite geometric sequences are used in various fields including finance for calculating perpetuities and in computer science for analyzing algorithms.