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  2. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    The area of a regular polygon is half its perimeter multiplied by the distance from its center to its sides, and because the sequence tends to a circle, the corresponding formula–that the area is half the circumference times the radius–namely, A = ⁠ 1 / 2 ⁠ × 2πr × r, holds for a circle.

  3. Circular mil - Wikipedia

    en.wikipedia.org/wiki/Circular_mil

    A circular mil is a unit of area, equal to the area of a circle with a diameter of one mil (one thousandth of an inch or 0.0254 mm). It is equal to π /4 square mils or approximately 5.067 × 10 −4 mm 2 .

  4. 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 ...

  5. Circumference - Wikipedia

    en.wikipedia.org/wiki/Circumference

    The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. [1] More generally, the perimeter is the curve length around any closed figure. Circumference may also refer to the circle itself, that is, the locus corresponding to the edge of a disk. The circumference of a sphere is the ...

  6. 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]

  7. 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, =

  8. Equivalent radius - Wikipedia

    en.wikipedia.org/wiki/Equivalent_radius

    The area-equivalent radius of a 2D object is the radius of a circle with the same area as the object Cross sectional area of a trapezoidal open channel, red highlights the wetted perimeter, where water is in contact with the channel. The hydraulic diameter is the equivalent circular configuration with the same circumference as the wetted perimeter.

  9. List of formulas in elementary geometry - Wikipedia

    en.wikipedia.org/wiki/List_of_formulas_in...

    Shape Area Perimeter/Circumference Meanings of symbols Square: is the length of a side Rectangle (+)is length, is breadth Circle: or : where is the radius and is the diameter ...