Question

radius of circle define

Answer 1

The radius of a circle is the length of the line from the center to any point on its edge. The plural form is radii. In the figure above, drag the orange dot around and see that the radius is always constant at any point on the circle.

Answer 2

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also the length of any of them. The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel.