Series & Sequences Calculator

Evaluate sums of arithmetic, geometric and Taylor series with full working.

About this calculator

A series calculator evaluates the sum of finite or infinite series, including arithmetic, geometric, and Taylor/Maclaurin series. The calculator also tests convergence using standard criteria (ratio test, root test, comparison test, integral test).

Series are how every transcendental function is computed in software: sin(x), eˣ, ln(x) are all evaluated using their Taylor series at the desired x. Understanding series is also crucial in signal processing (Fourier series) and probability (generating functions).

Formula

\sum_{n=0}^{\infty} \frac{x^n}{n!} = e^x

  • Taylor — f(x) = Σ f^(n)(a)·(x−a)ⁿ/n!
  • Convergence — Ratio test: lim |aₙ₊₁/aₙ|; <1 converges
  • Geometric — Σ rⁿ = 1/(1−r) for |r| < 1

Worked example

Inputs: Sum the geometric series 1 + 1/2 + 1/4 + 1/8 + ...

  1. First term a = 1, common ratio r = 1/2
  2. |r| < 1, so series converges
  3. Sum = a / (1 − r) = 1 / 0.5 = 2
  4. Famous example: each step is half the remaining distance, so the total is finite

Frequently asked questions

How do computers compute sin(x)?

Modern processors use the Taylor series sin(x) = x − x³/6 + x⁵/120 − x⁷/5040 + ..., truncated to enough terms for the required precision. Argument reduction first maps x into [−π/4, π/4] for fastest convergence, then 6–10 terms of the series provide IEEE 754 double precision. Hardware sometimes uses a CORDIC algorithm instead, which is more efficient for digital logic.

Does 1 − 1 + 1 − 1 + ... have a sum?

Classically no — the partial sums oscillate between 0 and 1 and never settle. However, certain generalised summation methods (Cesàro, Abel) assign this series a value of 1/2, which is mathematically consistent and useful in physics (regularisation of divergent integrals). This is the spirit of Ramanujan summation.

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