A space geometry, in which a semicircle rotates a Zhou Suocheng around a straight line equivalent to its diameter, is called a sphere, and the radius of the semicircle is the radius of the sphere. A sphere is a three-dimensional figure with only one continuous surface, which is called a sphere. The orthographic projection of a sphere on any plane is a circle with the same size, and the diameter of the projected circle is equal to the diameter of the sphere.
Extended data:
1, the straight line connecting the center of the sphere and the center of the section is perpendicular to the section.
2. The distance d from the center of the sphere to the cross section has the following relations with the radius r of the sphere and the radius r of the cross section: r? =R？ -Dee?
3. A circle whose sphere is cut by a plane passing through the center of the sphere is called a great circle, and a circle cut by a section not passing through the center of the sphere is called a small circle.
4. On the sphere, the length of the shortest connecting line between two points is the length of a bad arc passing through the great circle between these two points. We call this arc length the spherical distance between two points.