According to the data of Quick Solution Encyclopedia, radius is a term in mathematical geometry. The radius of a geometric figure is usually the radius of the largest circle or ball contained in it. In classical geometry, the radius of a circle or circle is an arbitrary line segment from the center of the circle to the circumference. The typical abbreviation and mathematical variable name of radius is r, and by extension, the diameter d is defined as twice the radius: d=2r.

Diameter refers to the distance from the center of a plane figure or a solid (such as a circle, a cone section, a ball or a cube) to two points on the side, usually represented by the letter "D". A straight line connecting two points on the circumference and passing through the center of the circle is called the diameter of the circle, and a straight line connecting two points on the sphere and passing through the center of the sphere is called the diameter of the sphere.