Radius

Uncommon card · No. 163636

In classical geometry, a radius (pl.: radii or radiuses) of a circle or sphere is any of the line segments from its center to its perimeter (circle) or surface (sphere), and, in more modern usage, it is also their length. The radius of a regular polygon is the line segment or distance from its center to any of its vertices. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel. The typical abbreviation and mathematical symbol for radius is R or r. By extension, the diameter (denoted D or d) is defined as twice the radius: d = 2 r ⇒ r = 1 2 d {\displaystyle d=2r\quad \Rightarrow \quad r={\frac {1}{2}}d} If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere. In either case, the radius may be...

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