radian
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When the length of an arc of a circle is equal to the radius of the circle, the angle subtended by that arc equals one radian.
ra·di·an
(rā′dē-ən)n. Abbr. rad
A unit of angular measure equal to the angle subtended at the center of a circle by an arc equal in length to the radius of the circle, approximately 57°17′44.6".
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
radian
(ˈreɪdɪən)n
(Units) 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. Symbol: rad
[C19: from radius]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
ra•di•an
(ˈreɪ di ən)n.
the measure of a central angle subtending an arc equal in length to the radius: equal to 57.2958°. Abbr.: rad
[1875–80]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
ra·di·an
(rā′dē-ən) A unit of angular measure equal to a little more than 57°. This is the measure of an angle whose vertex is the center of a circle and whose two rays intersect the circle so as to form an arc with the same length as the circle's radius.
The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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| Noun | 1. | radian - the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees) angular unit - a unit of measurement for angles milliradian - a unit of angular distance equal to one thousandth of a radian |
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