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Infinite Series

450 BCE (approx.)Ancient Greece (Zeno and Archimedes)

Concept

Can you add infinitely many things and get a finite sum? From Zeno to Euler's magical summations.

Understand it in one breath

"Adding infinitely many numbers can still give a finite answer." A celebrated example is 1 + 1/4 + 1/9 + 1/16 + … = π²/6 (Euler, 1735). Not every function equals its Taylor series, but analytic functions such as sin, cos, and exp do admit convergent power-series representations that support numerical computation.

At a glance

02468101200.511.52
y: ∑1/k²

Key formula

n=11n2=π261.6449\sum_{n=1}^{\infty} \dfrac{1}{n^2} = \dfrac{\pi^2}{6} \approx 1.6449

Key moments

450 BCE

Zeno’s paradox — Achilles and the tortoise

Can infinitely many stages be completed in finite time? Zeno turned the conceptual problem behind infinite series into a lasting philosophical challenge.

250 BCE

Archimedes — 1+1/4+1/16+… = 4/3

Archimedes summed a geometric series to find the area of a parabolic segment exactly, anticipating integral calculus by nearly two millennia.

1735 CE

Euler — 1+1/4+1/9+1/16+… = π²/6

Euler solved the Basel problem, revealing an astonishing link between the reciprocal squares of the integers and the geometry of the circle.

1873 CE

Weierstrass — rigorous convergence

Precise limit definitions replaced informal intuition about infinite sums and made convergence a central, testable property of a series.

Modern applications

Taylor series for computing sine and exponentials, Fourier series for signal decomposition, Dirichlet series in number theory, and perturbation theory in quantum fields.

Beyond MathVoyage

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