a unit of angle measure widely used in mathematics and science. One radian is the angle at the center of a circle that cuts off an arc of length equal to the radius. Since the circumference equals 2 pi times the radius, one radian equals 1/(2 pi) of the circle, or approximately 57.295 779°. Using radians to measure angles seems unnatural at first. However, when angles are stated in radians the constant pi tends to disappear from the equations, and this greatly simplifies calculation. For example, the length of an arc is simply its radius multiplied by its angular measure in radians, and the area of a sector of a circle is simply its angular measure in radians multiplied by half the square of the radius. The radian was defined and named by James Thomson in 1873. Thomson was a mathematics professor at Queen's College, Belfast, Northern Ireland, and the brother of the famous physicist William Thomson, Lord Kelvin.

Dictionary of units of measurement. 2015.

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  • radian — [ radjɑ̃ ] n. m. • 1904; mot angl. 1879; du lat. radius « rayon » ♦ Métrol. Unité de mesure d angle plan (symb.rad). 180° valent π radians. ⊗ HOM. Radiant. ● radian nom masculin ( …   Encyclopédie Universelle

  • radian — RADIÁN, radiani, s.m. Unitate de măsură pentru unghiuri, egală cu un unghi la centrul unui cerc cuprinzând un arc de cerc a cărui lungime este egală cu raza cercului [Pr:. di an] – Din fr. radian. Trimis de RACAI, 13.09.2007. Sursa: DEX 98 … …   Dicționar Român

  • Radián — Saltar a navegación, búsqueda El radián es la unidad de ángulo plano en el Sistema Internacional de Unidades. Representa el ángulo central en una circunferencia que subtiende un arco cuya longitud es igual a la del radio. Su símbolo es rad. Hasta …   Wikipedia Español

  • Rädian — Rädian, Gott der Lappländer, welcher die frommen Seelen der Verstorbenen zu sich in den Himmel nahm, daher der Aufenthalt der Guten auch Rädian Aimo genannt …   Pierer's Universal-Lexikon

  • radián — (Del ingl. radian, y este del lat. radius, radio1). m. Geom. Unidad de ángulo plano del Sistema Internacional equivalente a uno cuyo arco tiene igual longitud que el radio. (Símb. rad) …   Diccionario de la lengua española

  • radian — [rā′dē ən] n. [< RADIUS] the basic unit of plane angle in the SI system, equal to 57°, 17′, 44.8″ (57.29578°, the angle formed at the center of a circle by two radii cutting off an arc whose length is equal to the radius of the circle): one… …   English World dictionary

  • Radian — Ra di*an (r[=a] d[i^]*an), n. [From {Radius}.] (Math.) An arc of a circle which is equal to the radius, or the angle measured by such an arc. [1913 Webster] …   The Collaborative International Dictionary of English

  • radian — 1879, from RADIUS (Cf. radius) …   Etymology dictionary

  • radián — sustantivo masculino 1. Área: geometría Unidad de medida de ángulos que corresponde al ángulo central de una circunferencia en el que la longitud del arco y la del radio son iguales …   Diccionario Salamanca de la Lengua Española

  • radian — ► NOUN ▪ a unit of measurement of angles equal to about 57.3°, equivalent to the angle subtended at the centre of a circle by an arc equal in length to the radius …   English terms dictionary

  • Radian — For other uses, see Radian (disambiguation). mrad redirects here. For millirads, see Rad (unit). An angle of 1 rad …   Wikipedia

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