Circle

Circle
Circle-withsegments.svg
A circle (black), which is measured by its circumference (C), diameter (D) in cyan, and radius (R) in red; its centre (O) is in magenta.

A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.

A circle is a simple closed curve that divides the plane into two regions: an interior and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is only the boundary and the whole figure is called a disc.

A circle may also be defined as a special kind of ellipse in which the two foci are coincident and the eccentricity is 0, or the two-dimensional shape enclosing the most area per unit perimeter squared, using calculus of variations.

Euclid's definition

A circle is a plane figure bounded by one line, and such that all right lines drawn from a certain point within it to the bounding line, are equal. The bounding line is called its circumference and the point, its centre.

— Euclid, Elements, Book I[1]:4
Other Languages
Afrikaans: Sirkel
Alemannisch: Kreis (Geometrie)
አማርኛ: ክብ
العربية: دائرة
aragonés: Circumferencia
armãneashti: Țercľiu
অসমীয়া: বৃত্ত
asturianu: Circunferencia
Aymar aru: Muyu
azərbaycanca: Çevrə
تۆرکجه: دایره
বাংলা: বৃত্ত
Bân-lâm-gú: Îⁿ-hêng
беларуская: Акружнасць
беларуская (тарашкевіца)‎: Акружына
български: Окръжност
bosanski: Kružnica
brezhoneg: Kelc'h
Чӑвашла: Çавракăш
čeština: Kružnice
chiShona: Denderedzwa
Cymraeg: Cylch
dansk: Cirkel
Deutsch: Kreis
dolnoserbski: Cera krejza
eesti: Ringjoon
Ελληνικά: Κύκλος
emiliàn e rumagnòl: Serć (giumetrìa)
español: Circunferencia
Esperanto: Cirklo
euskara: Zirkulu
فارسی: دایره
Fiji Hindi: Circle
føroyskt: Sirkul
français: Cercle
Gaeilge: Ciorcal
Gaelg: Kiarkyl
Gàidhlig: Cearcall
galego: Círculo
贛語: 圓形
ગુજરાતી: વર્તુળ
한국어: 원 (기하학)
Հայերեն: Շրջանագիծ
हिन्दी: वृत्त
hornjoserbsce: Kružnica
hrvatski: Kružnica
Ido: Cirklo
Bahasa Indonesia: Lingkaran
interlingua: Circulo
isiXhosa: Isazinge
italiano: Circonferenza
עברית: מעגל
Basa Jawa: Bunderan
ქართული: წრეწირი
қазақша: Шеңбер
Kiswahili: Duara
Kreyòl ayisyen: Sèk (non)
kurdî: Gilover
لۊری شومالی: دایره
Latina: Circulus
latviešu: Riņķa līnija
Lëtzebuergesch: Krees (Geometrie)
lietuvių: Apskritimas
Limburgs: Cirkel
lumbaart: Sércc
македонски: Кружница
മലയാളം: വൃത്തം
मराठी: वर्तुळ
مصرى: دايره
Bahasa Melayu: Bulatan
монгол: Тойрог
မြန်မာဘာသာ: စက်ဝိုင်း
Nederlands: Cirkel
नेपाली: वृत
नेपाल भाषा: चाकः
日本語: 円 (数学)
Nordfriisk: Kreis (geometrii)
Norfuk / Pitkern: Sirkil
norsk: Sirkel
norsk nynorsk: Sirkel
occitan: Cercle
олык марий: Оҥго
ଓଡ଼ିଆ: ବୃତ୍ତ
oʻzbekcha/ўзбекча: Aylana
ਪੰਜਾਬੀ: ਚੱਕਰ
پنجابی: چکر
پښتو: گردکه
Patois: Soerkl
ភាសាខ្មែរ: រង្វង់
Plattdüütsch: Krink
polski: Okrąg
português: Circunferência
română: Cerc
Runa Simi: P'allta muyu
русиньскый: Круг
русский: Окружность
Scots: Raing
shqip: Rrethi
Simple English: Circle
slovenčina: Kružnica
slovenščina: Krožnica
Soomaaliga: Goobo
српски / srpski: Кружница
srpskohrvatski / српскохрватски: Kružnica
suomi: Ympyrä
svenska: Cirkel
Tagalog: Bilog
தமிழ்: வட்டம்
татарча/tatarça: Әйләнә
Türkçe: Çember
українська: Коло
اردو: دائرہ
Vahcuengh: Luenz
vèneto: Sercio
Tiếng Việt: Đường tròn
文言:
Winaray: Lidong
吴语:
ייִדיש: קרייז
Yorùbá: Òbìrípo
粵語: 圓形
žemaitėška: Apskrėtėms
中文: