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This part of the extended data mainly examines the knowledge points of diameter:

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

The diameter is a line segment passing through the center of the circle with both ends at any point on the circle. Generally represented by the letter d (diameter). A straight line with a diameter is the symmetry axis of a circle.

The two endpoints of the diameter are on a circle, and the center of the circle is the midpoint of the diameter. Diameter divides a circle into two parts with equal area, and the middle line segment is called diameter (each part becomes a semicircle).