# radian

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## radian

an SI unit of plane angle; the angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius. 1 radian is equivalent to 57.296 degrees and π/2 radians equals a right angle

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

## radian

(**ray**-dee-ăn) A unit of angle used in plane geometry that is the angle subtended at the center of a circle by an arc of the circle equal in length to the circle's radius. Thus 2π radians equals 360°, 1 radian equals 57°.296, and 1° equals 0.017 radians. Solid angles, used in spherical geometry, are measured in steradians.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

The following article is from

*The Great Soviet Encyclopedia*(1979). It might be outdated or ideologically biased.## Radian

the central angle subtended in a circle by an arc whose length is equal to the circle’s radius. A radian is approximately equal to 57°17′44.8″. The radian is used as the unit of measurement of angles in what is known as circular, or radian, measure. If the circular measure of an angle is *a* radians, the angle contains (180*a/π*)°. Conversely, if the degree measure of an angle is *n°*, the circular measure is *πn*/180 radians. For example, angles of 30°, 45°, 60°, 90°, and 180° correspond to angles of *π*/6, *π*/4, *π*/3, *π*/2, and *π* radians, respectively.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

## radian

[′rād·ē·ən] (mathematics)

The central angle of a circle determined by two radii and an arc joining them, all of the same length.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## radian

The angle subtended at the center of a circle by an arc equal in length to its radius. A radian is an SI (Système international d'unités, or international system) unit most commonly used in sight calculations and other aiming problems. Its short form is

*rad*, and its value is equal to 57°17'44.8”, or one rad = 57.2958°.An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved