What is 半徑 in English?

radius=半徑
diameter=直徑
cercumference=圓周

radius(單數)

or

radii(眾數)

radius
the simply is r
2r = diameter
2兀r = 圓周

Radius

半徑 in English is "r a d i u s"

Radius

In classical geometry, a radius of a circle or sphere is any line segment from its center to its boundary. 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 is commonly used as a synonym for radius.

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/CIRCLE_1.svg/180px-CIRCLE_1.svg.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
Circle illustration

在一個圓中，從圓心到圓周上任何一點的距離被稱為半徑；在數學裡常以 r 來表示其長度。
在圓里，半徑與該圓的切線垂直。半徑等於該圓直徑的二分之一。在圓里，面積與半徑的平方的比值為π，即圓周率。
另，一個球的半徑即是任一過該球球心的圓的半徑。

RADIUS

radius 圓周的半徑

Radius = 半徑
Diameter = 2 times 半徑