Radius

The radius of a circle

In geometry, the radius of a circle or sphere, written as $r$ ,^[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 ${\displaystyle r}$ and the circumference ${\displaystyle c}$ of a circle is $~c=2\pi r.$

The area ${\displaystyle A}$ of a circle of radius ${\displaystyle r}$ is ${\displaystyle ~A=\pi r^{2}.}$

Related pages[change | change source]

References[change | change source]

↑ "List of Geometry and Trigonometry Symbols". Math Vault. 2020-04-17. Retrieved 2020-09-24.{{cite web}}: CS1 maint: url-status (link)
↑ Weisstein, Eric W. "Radius". mathworld.wolfram.com. Retrieved 2020-09-24.
↑ "Radius, diameter, & circumference | Circles (article)". Khan Academy. Retrieved 2020-09-24.

Other websites[change | change source]

Definition and properties of the radius of a circle with interactive applet

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[1] "List of Geometry and Trigonometry Symbols". Math Vault. 2020-04-17. Retrieved 2020-09-24.{{cite web}}: CS1 maint: url-status (link)

[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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