Pi Recipes | Britannica
To Eudoxus of Cnidus (c. 400–350 bce) goes the honour of being the first to show that the area of a circle is proportional to the square of its radius. In today’s algebraic notation, that proportionality is expressed by the familiar formula A = πr2. Yet the constant of proportionality, π, despite its familiarity, is highly mysterious, and the quest to understand it and find its exact value has occupied mathematicians for thousands of years. A century after Eudoxus, Archimedes found the first good approximation of π: 31071
Source: britannica.com