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  2. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    A diameter of an ellipse is any line passing through the centre of the ellipse. [2] 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. [3] The longest diameter is called the major axis.

  3. Pi - Wikipedia

    en.wikipedia.org/wiki/Pi

    The number π (/ p aɪ /; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.

  4. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    For a cyclic quadrilateral, the exterior angle is equal to the interior opposite angle. An inscribed angle subtended by a diameter is a right angle (see Thales' theorem). The diameter is the longest chord of the circle. Among all the circles with a chord AB in common, the circle with minimal radius is the one with diameter AB.

  5. Equivalent radius - Wikipedia

    en.wikipedia.org/wiki/Equivalent_radius

    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. [1] Diameter at breast height is the circumference of tree trunk, measured at height of 4.5 feet, divided by pi. This corresponds to the 1D mean diameter.

  6. 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.

  7. Curve of constant width - Wikipedia

    en.wikipedia.org/wiki/Curve_of_constant_width

    A curve of constant width defined by an 8th-degree polynomial. Circles have constant width, equal to their diameter.On the other hand, squares do not: supporting lines parallel to two opposite sides of the square are closer together than supporting lines parallel to a diagonal.

  8. Diameter (disambiguation) - Wikipedia

    en.wikipedia.org/wiki/Diameter_(disambiguation)

    Diameter (group theory), the maximum diameter of a Cayley graph of the group; Equivalent diameter, the diameter of a circle or sphere with the same area, perimeter, or volume as another object; Hydraulic diameter, the equivalent diameter of a tube or channel for fluids; Kinetic diameter, a measure of particles in a gas related to the mean free path

  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]