This article is about the shape and mathematical concept. For other uses, see Circle (disambiguation).
"360 degrees" and "360°" redirect here. For other uses, see 360 degrees (disambiguation).
Circle
A circle
circumference C
diameter D
radius R
centre or origin O
Type
Conic section
Symmetry group
O(2)
Area
πR2
Perimeter
C = 2πR
Geometry
Projecting a sphere to a plane
Outline
History (Timeline)
Branches
Euclidean
Non-Euclidean
Elliptic
Spherical
Hyperbolic
Non-Archimedean geometry
Projective
Affine
Synthetic
Analytic
Algebraic
Arithmetic
Diophantine
Differential
Riemannian
Symplectic
Discrete differential
Complex
Finite
Discrete/Combinatorial
Digital
Convex
Computational
Fractal
Incidence
Noncommutative geometry
Noncommutative algebraic geometry
Concepts
Features
Dimension
Straightedge and compass constructions
Angle
Curve
Diagonal
Orthogonality (Perpendicular)
Parallel
Vertex
Congruence
Similarity
Symmetry
Zero-dimensional
Point
One-dimensional
Line
segment
ray
Length
Two-dimensional
Plane
Area
Polygon
Triangle
Altitude
Hypotenuse
Pythagorean theorem
Parallelogram
Square
Rectangle
Rhombus
Rhomboid
Quadrilateral
Trapezoid
Kite
Circle
Diameter
Circumference
Area
Three-dimensional
Volume
Cube
cuboid
Cylinder
Dodecahedron
Icosahedron
Octahedron
Pyramid
Platonic Solid
Sphere
Tetrahedron
Four- / other-dimensional
Tesseract
Hypersphere
Geometers
by name
Aida
Aryabhata
Ahmes
Alhazen
Apollonius
Archimedes
Atiyah
Baudhayana
Bolyai
Brahmagupta
Cartan
Coxeter
Descartes
Euclid
Euler
Gauss
Gromov
Hilbert
Huygens
Jyeṣṭhadeva
Kātyāyana
Khayyám
Klein
Lobachevsky
Manava
Minkowski
Minggatu
Pascal
Pythagoras
Parameshvara
Poincaré
Riemann
Sakabe
Sijzi
al-Tusi
Veblen
Virasena
Yang Hui
al-Yasamin
Zhang
List of geometers
by period
BCE
Ahmes
Baudhayana
Manava
Pythagoras
Euclid
Archimedes
Apollonius
1–1400s
Zhang
Kātyāyana
Aryabhata
Brahmagupta
Virasena
Alhazen
Sijzi
Khayyám
al-Yasamin
al-Tusi
Yang Hui
Parameshvara
1400s–1700s
Jyeṣṭhadeva
Descartes
Pascal
Huygens
Minggatu
Euler
Sakabe
Aida
1700s–1900s
Gauss
Lobachevsky
Bolyai
Riemann
Klein
Poincaré
Hilbert
Minkowski
Cartan
Veblen
Coxeter
Present day
Atiyah
Gromov
v
t
e
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 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 machinery possible. In mathematics, the study of the circle has helped inspire the development of geometry, astronomy and calculus.
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