# Geometric series

In mathematics, a **geometric series** is the sum of an infinite number of terms that have a constant ratio between successive terms. For example, the series

is geometric, because each successive term can be obtained by multiplying the previous term by 1/2. In general, a geometric series is written as *a* + *ar* + *ar*^{2} + *ar*^{3} + ... , where *a* is the coefficient of each term and *r* is the common ratio between adjacent terms. Geometric series are among the simplest examples of infinite series and can serve as an introduction to Taylor series and Fourier series. Geometric series had an important role in the early development of calculus, are used throughout mathematics, and have important applications in physics, engineering, biology, economics, computer science, queueing theory, and finance.

The name geometric series indicates each term is the geometric mean of its two neighboring terms, similar to how the name arithmetic series indicates each term is the arithmetic mean of its two neighboring terms. The sequence of geometric series terms (without any of the additions) is called a geometric sequence or, equivalently, a geometric progression.