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  2. Pi - Wikipedia

    en.wikipedia.org/wiki/Pi

    The first computational formula for π, based on infinite series, was discovered a millennium later. [1] [2] The earliest known use of the Greek letter π to represent the ratio of a circle's circumference to its diameter was by the Welsh mathematician William Jones in 1706. [3]

  3. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for the diameter of a sphere.

  4. List of formulae involving π - Wikipedia

    en.wikipedia.org/wiki/List_of_formulae_involving_π

    where C is the circumference of a circle, d is the diameter, and r is the radius. More generally, = where L and w are, respectively, the perimeter and the width of any curve of constant width. = where A is the area of a circle. More generally, =

  5. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    Here, the Greek letter π represents the constant ratio of the circumference of any circle to its diameter, approximately equal to 3.14159. One method of deriving this formula, which originated with Archimedes, involves viewing the circle as the limit of a sequence of regular polygons with an increasing number of sides

  6. Liu Hui's π algorithm - Wikipedia

    en.wikipedia.org/wiki/Liu_Hui's_π_algorithm

    Liu Hui's method of calculating the area of a circle. Liu Hui's π algorithm was invented by Liu Hui (fl. 3rd century), a mathematician of the state of Cao Wei.Before his time, the ratio of the circumference of a circle to its diameter was often taken experimentally as three in China, while Zhang Heng (78–139) rendered it as 3.1724 (from the proportion of the celestial circle to the diameter ...

  7. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    A circle of radius 1 (using this distance) is the von Neumann neighborhood of its centre. A circle of radius r for the Chebyshev distance (L ∞ metric) on a plane is also a square with side length 2r parallel to the

  8. Measurement of a Circle - Wikipedia

    en.wikipedia.org/wiki/Measurement_of_a_Circle

    A page from Archimedes' Measurement of a Circle. Measurement of a Circle or Dimension of the Circle (Greek: Κύκλου μέτρησις, Kuklou metrēsis) [1] is a treatise that consists of three propositions, probably made by Archimedes, ca. 250 BCE. [2] [3] The treatise is only a fraction of what was a longer work. [4] [5]

  9. Approximations of π - Wikipedia

    en.wikipedia.org/wiki/Approximations_of_π

    This is 'approximately' the circumference of a circle whose diameter is 20,000. — Āryabhaṭīya Approximating π to four decimal places: π ≈ 62832 ⁄ 20000 = 3.1416, [ 18 ] [ 19 ] [ 20 ] Aryabhata stated that his result "approximately" ( āsanna "approaching") gave the circumference of a circle.