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  2. Equivalent radius - Wikipedia

    en.wikipedia.org/wiki/Equivalent_radius

    For example, a square of side L has a perimeter of . Setting that perimeter to be equal to that of a circle imply that = Applications: US hat size is the circumference of the head, measured in inches, divided by pi, rounded to the nearest 1/8 inch. This corresponds to the 1D mean diameter.

  3. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    Following Archimedes' argument in The Measurement of a Circle (c. 260 BCE), compare the area enclosed by a circle to a right triangle whose base has the length of the circle's circumference and whose height equals the circle's radius. If the area of the circle is not equal to that of the triangle, then it must be either greater or less.

  4. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    Since the diameter is twice the radius, the "missing" part of the diameter is (2r − x) in length. Using the fact that one part of one chord times the other part is equal to the same product taken along a chord intersecting the first chord, we find that (2r − x)x = (y / 2) 2. Solving for r, we find the required result.

  5. List of formulae involving π - Wikipedia

    en.wikipedia.org/wiki/List_of_formulae_involving_π

    where A is the area of a squircle with minor radius r, is the gamma function. A = ( k + 1 ) ( k + 2 ) π r 2 {\displaystyle A=(k+1)(k+2)\pi r^{2}} where A is the area of an epicycloid with the smaller circle of radius r and the larger circle of radius kr ( k ∈ N {\displaystyle k\in \mathbb {N} } ), assuming the initial point lies on the ...

  6. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    In this context, a diameter is any chord which passes through the conic's centre. A diameter of an ellipse is any line passing through the centre of the ellipse. [7] Half of any such diameter may be called a semidiameter, although this term is most often a synonym for the radius of a circle or sphere. [8] The longest diameter is called the ...

  7. Sphere - Wikipedia

    en.wikipedia.org/wiki/Sphere

    where r is the radius and d is the diameter of the sphere. Archimedes first derived this formula by showing that the volume inside a sphere is twice the volume between the sphere and the circumscribed cylinder of that sphere (having the height and diameter equal to the diameter of the sphere). [6]

  8. Equivalent spherical diameter - Wikipedia

    en.wikipedia.org/wiki/Equivalent_spherical_diameter

    In other terms, it is the length of the line dividing the projection in two areas of equal surfaces. The area-equivalent diameter D A, also termed circular-equivalent diameter, is the diameter of a sphere having the same projected area as the particle's projection. Enabled by the introduction of digital image analysis, this corresponds to a ...

  9. Circumference - Wikipedia

    en.wikipedia.org/wiki/Circumference

    In geometry, the circumference (from Latin circumferens, meaning "carrying around") is the perimeter of a circle or ellipse.The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. [1]