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  2. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    A circle bounds a region of the plane called a disc. The circle has been known since before the beginning of recorded history. Natural circles are common, such as the full moon or a slice of round fruit. The circle is the basis for the wheel, which, with related inventions such as gears, makes much of modern

  3. History of geometry - Wikipedia

    en.wikipedia.org/wiki/History_of_geometry

    Parameshvara Nambudiri was the first mathematician to give a formula for the radius of the circle circumscribing a cyclic quadrilateral. [22] The expression is sometimes attributed to Lhuilier [1782], 350 years later. With the sides of the cyclic quadrilateral being a, b, c, and d, the radius R of the circumscribed circle is:

  4. Roundabout - Wikipedia

    en.wikipedia.org/wiki/Roundabout

    The Hotel Indonesia Roundabout in Jakarta, Indonesia A magic roundabout in Kent, UK, on the A13 road near Sadlers Farm. A roundabout, a rotary and a traffic circle are types of circular intersection or junction in which road traffic is permitted to flow in one direction around a central island, and priority is typically given to traffic already in the junction.

  5. Unit circle - Wikipedia

    en.wikipedia.org/wiki/Unit_circle

    Since C = 2πr, the circumference of a unit circle is 2π. In mathematics, a unit circle is a circle of unit radius—that is, a radius of 1. [1] Frequently, especially in trigonometry, the unit circle is the circle of radius 1 centered at the origin (0, 0) in the Cartesian coordinate system in the Euclidean plane.

  6. Timeline of geometry - Wikipedia

    en.wikipedia.org/wiki/Timeline_of_geometry

    260 BC – Archimedes proved that the value of π lies between 3 + 1/7 (approx. 3.1429) and 3 + 10/71 (approx. 3.1408), that the area of a circle was equal to π multiplied by the square of the radius of the circle and that the area enclosed by a parabola and a straight line is 4/3 multiplied by the area of a triangle with equal base and height ...

  7. History of mathematics - Wikipedia

    en.wikipedia.org/wiki/History_of_mathematics

    It created mathematical proof for the Pythagorean theorem, [112] and a mathematical formula for Gaussian elimination. [113] The treatise also provides values of π , [ 107 ] which Chinese mathematicians originally approximated as 3 until Liu Xin (d. 23 AD) provided a figure of 3.1457 and subsequently Zhang Heng (78–139) approximated pi as 3. ...

  8. Circles of Apollonius - Wikipedia

    en.wikipedia.org/wiki/Circles_of_Apollonius

    Similarly, the circle is defined as the unique circle passing through the triangle vertex that maintains a constant ratio of distances to the other two vertices and , and so on for the circle . All three circles intersect the circumcircle of the triangle orthogonally .

  9. William Jones (mathematician) - Wikipedia

    en.wikipedia.org/wiki/William_Jones_(mathematician)

    William Jones, FRS (1675 – 1 July 1749 [1]) was a Welsh mathematician best known for his use of the symbol π (the Greek letter Pi) to represent the ratio of the circumference of a circle to its diameter. He was a close friend of Sir Isaac Newton and Sir Edmund Halley.