Radius 1780815 220856674 2008-06-21T23:06:40Z 122.106.242.51 /* Circles */ {{otheruses}} == Circles == [[Image:CIRCLE 1.svg|thumb|Circle illustration]] In classical [[geometry]], a '''radius''' (plural: radii) of a [[circle]] or [[sphere]] is any [[line segment]] from its center to its [[perimeter]]. By extension, '''''the'' radius''' of a circle or sphere is the [[length]] of any such segment. The radius is half the [[diameter]]. In science and engineering the term [[Radius_of_curvature|radius of curvature]] is commonly used as a synonym for radius. More generally&mdash;in [[geometry]], [[engineering]], [[graph theory]], and many other contexts&mdash;the radius of something (e.g., a [[cylinder (geometry)|cylinder]], a [[polygon]], a [[graph theory|graph]], or a mechanical part) is the [[distance]] from its [[center (geometry)|center]] or [[axis of symmetry]] to its outermost points. In this case, the radius may be more than half the diameter. The relationship between the radius and the [[circumference]] of a circle is <math>r=\frac{c}{2\pi}</math>. To compute the radius of a circle going through three points <math> P_1, P_2, P_3</math>, the following formula can be used: : <math>r=\frac{|P_1-P_3|}{2\sin\theta}</math> where <math>\theta</math> is the angle <math> \angle P_1 P_2 P_3.</math> A more simple way to find the length of the radius is: : <math>r=\frac{diameter}{2}</math> A radius may also be applied to [[arithmetic]]. Where 4,5,6,7,8,9 and 10 can be in a three number radius of 7. == Polygons == Regular polygons are sometimes said to have a radius, defined as the distance from the center to a vertex. This is the same as the radius of a circumscribed circle with the same center. This latter formulation is sometimes used to define the radius of an arbitrary polygon and is called the circumradius. == See also== *[[Radius (bone)]] *[[Radius of convergence]] [[Category:Geometry]] [[ar:نصف قطر]] [[ast:Radiu (xeometría)]] [[zh-min-nan:Poàⁿ-kèng]] [[bs:Poluprečnik]] [[bg:Радиус]] [[ca:Radi (geometria)]] [[cv:Радиус]] [[cs:Poloměr]] [[da:Radius (cirkel)]] [[de:Radius]] [[el:Ακτίνα (γεωμετρία)]] [[es:Radio (geometría)]] [[eo:Radiuso]] [[eu:Erradio (geometria)]] [[fr:Rayon (géométrie)]] [[gl:Raio (xeometría)]] [[ko:반지름]] [[id:Radius]] [[is:Geisli (rúmfræði)]] [[it:Raggio (geometria)]] [[he:רדיוס]] [[sw:Nusukipenyo]] [[lv:Rādiuss]] [[lb:Radius]] [[lt:Spindulys]] [[mk:Радиус]] [[nl:Straal (wiskunde)]] [[ja:半径]] [[no:Radius]] [[nn:Radius]] [[pl:Promień]] [[pt:Raio]] [[ro:Rază]] [[qu:Illwa]] [[ru:Радиус]] [[simple:Radius]] [[sk:Polomer (kružnica)]] [[sl:Polmer]] [[sr:Полупречник]] [[fi:Säde]] [[sv:Radie]] [[ta:ஆரம்]] [[th:รัศมี]] [[vi:Bán kính]] [[tr:Yarıçap]] [[uk:Радіус]] [[zh:半径]]