The radius of a circle

In geometry, the radius of a circle or sphere, written as [math]\displaystyle{ r }[/math],[1] is the shortest connection between the center and the boundary. It is either the distance from the center to the perimeter (in the case of a circle), or the distance from the center to the surface (in the case of a sphere). It is half of the diameter.[2] That is, when r is the radius and d is the diameter:[3]

r = d ÷ 2

d = 2 x r = r + r

The relationship between the radius [math]\displaystyle{ {\displaystyle r} }[/math] and the circumference [math]\displaystyle{ {\displaystyle c} }[/math] of a circle is [math]\displaystyle{ ~c = 2\pi r. }[/math]

The area [math]\displaystyle{ {\displaystyle A} }[/math] of a circle of radius [math]\displaystyle{ {\displaystyle r} }[/math] is [math]\displaystyle{ {\displaystyle ~A = \pi r^2.} }[/math]

Radius Media

Related pages


  1. "List of Geometry and Trigonometry Symbols". Math Vault. 2020-04-17. Retrieved 2020-09-24.
  2. Weisstein, Eric W. "Radius". mathworld.wolfram.com. Retrieved 2020-09-24.
  3. "Radius, diameter, & circumference | Circles (article)". Khan Academy. Retrieved 2020-09-24.

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