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  2. 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, =

  3. Machin-like formula - Wikipedia

    en.wikipedia.org/wiki/Machin-like_formula

    In mathematics, Machin-like formulas are a popular technique for computing π (the ratio of the circumference to the diameter of a circle) to a large number of digits. They are generalizations of John Machin 's formula from 1706:

  4. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    Conjugate diameters are a pair of diameters where one is parallel to a tangent to the ellipse at the endpoint of the other diameter. The diameter of a circle is exactly twice its radius. However, this is true only for a circle, and only in the Euclidean metric. Jung's theorem provides more general inequalities relating the diameter to the radius.

  5. Zeiss formula - Wikipedia

    en.wikipedia.org/wiki/Zeiss_formula

    The formula is = /, where is the diagonal measure of a camera format, film, sensor, or print, and the maximum acceptable diameter of the circle of confusion. The Zeiss formula is apocryphal, in the sense that it has grown to be a well-known named concept by propagation through the internet, even though it has no official origin, little ...

  6. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    Given a chord of length y and with sagitta of length x, since the sagitta intersects the midpoint of the chord, we know that it is a part of a diameter of the circle. Since the diameter is twice the radius, the "missing" part of the diameter is (2r − x) in length.

  7. 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 ...

  8. Equivalent radius - Wikipedia

    en.wikipedia.org/wiki/Equivalent_radius

    The hydraulic diameter is the equivalent circular configuration with the same circumference as the wetted perimeter. The area of a circle of radius R is . Given the area of a non-circular object A, one can calculate its area-equivalent radius by setting = or, alternatively:

  9. 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]