Radian

<p>The radian, denoted by the symbol rad, is the unit of <a href="/facts/Angle/gFUTEQYq">angle</a> in the <a href="/facts/International_System_of_Units/S7YLglNz">International System of Units</a> (SI) and is the standard unit of angular measure used in many areas of <a href="/facts/Mathematics/pxTouaz4">mathematics</a>. It is defined such that one radian is the angle subtended at the centre of a circle by an <a href="/facts/Circular_arc/RrehhCQR">arc</a> that is equal in length to the radius. The unit was formerly an <a href="/facts/SI_supplementary_unit/RLu52lWy">SI supplementary unit</a> and is currently a <a href="/facts/Dimensionless_unit/TINrpQIq">dimensionless</a> <a href="/facts/SI_derived_unit/RLu52lWy">SI derived unit</a>, defined in the SI as 1 rad = 1 and expressed in terms of the <a href="/facts/SI_base_unit/M7PsTWg4">SI base unit</a> <a href="/facts/Metre/hPhzc1CV">metre</a> (m) as rad = m/m. Angles without explicitly specified units are generally assumed to be measured in radians, especially in mathematical writing.
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Radian open-in-new

Radian