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  2. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    Geometry. In geometry, a pp 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. In more modern usage, the length of a diameter is also called the diameter.

  3. Pi - Wikipedia

    en.wikipedia.org/wiki/Pi

    t. e. The number π (/ paɪ /; spelled out as " pi ") is a mathematical constant that is the ratio of a circle 's circumference to its diameter, approximately equal to 3.14159. The number π appears in many formulae across mathematics and physics.

  4. Sphere - Wikipedia

    en.wikipedia.org/wiki/Sphere

    The intersection of a sphere with an elliptic or hyperbolic cylinder whose axis passes through the sphere center. The locus of points whose sum or difference of great-circle distances from a pair of foci is a constant. Many theorems relating to planar conic sections also extend to spherical conics.

  5. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    The conventional definition in pre-calculus geometry is the ratio of the circumference of a circle to its diameter: π = C D . {\displaystyle \pi ={\frac {C}{D}}.} However, because the circumference of a circle is not a primitive analytical concept, this definition is not suitable in modern rigorous treatments.

  6. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    C = 2πR. A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. The distance between any point of the circle and the centre is called the radius. The length of a line segment connecting two points on the circle and passing through the centre is called the diameter.

  7. 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 ...

  8. Radian - Wikipedia

    en.wikipedia.org/wiki/Radian

    One radian is defined as the angle at the center of a circle which subtends an arc whose length equals the radius of the circle. [6] More generally, the magnitude in radians of a subtended angle is equal to the ratio of the arc length to the radius of the circle; that is, =, where θ is the subtended angle in radians, s is arc length, and r is radius.

  9. Semicircle - Wikipedia

    en.wikipedia.org/wiki/Semicircle

    PR is the diameter of a circle centered on O; its radius AO is the arithmetic mean of a and b. Using the geometric mean theorem, triangle PGR's altitude GQ is the geometric mean. For any ratio a:b, AO ≥ GQ. A semicircle can be used to construct the arithmetic and geometric means of two lengths using straight-edge and compass.