# A Geometric Proof of Machin's Formula

by Roger B. Nelsen (Lewis and Clark College)

Mathematics Magazine
December, 1990

Subject classification(s): Geometric Proof | Geometry and Topology | Famous Problems | Number Theory | Algebra and Number Theory
Applicable Course(s): 4.8 History of Math | 4.1 Introduction to Proofs | 3.2 Mainstream Calculus II

The author presents a geometric proof of Machin's formula, which expresses $$\frac {\pi}{4}$$ as the difference of two inverse tangent functions.

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