In a plane, a closed curve formed by rotating around a point for a certain length is called a circle. On the plane, a circle is a set of points whose distance from a fixed point is equal to a fixed length, which is called a circle.
A circle has countless axes of symmetry, which pass through the center of the circle. A circle has rotation invariance. A circle is a conic curve, which is obtained by cutting a cone from a plane parallel to the bottom of the cone.
The ratio of circumference to diameter of a circle is called pi, that is, pi = circumference/diameter. It is an infinite acyclic decimal, usually expressed by the letter π pronounced pà i. The arc larger than the semicircle is called the optimal arc, and the arc smaller than the semicircle is called the suboptimal arc, so the semicircle is neither the optimal arc nor the suboptimal arc. The optimal arc is generally represented by three letters, and the suboptimal arc is generally represented by two letters.
The arc is an arc with a central angle greater than 180 degrees, and the lower arc is an arc with a central angle less than 180 degrees. In the same circle or equal circle, two arcs that can overlap each other are called equal arcs. The angle of the vertex on the center of the circle is called the central angle, and the degree of the central angle is equal to the degree of the opposite arc.
The angle at which the vertex is on the circumference and both sides intersect with the circle is called the circumferential angle. The circumferential angle is equal to half the central angle of the same arc and half the degree of the arc. A circle in which two equal circles can overlap is called an equal circle. Concentric circles A circle with the same center is called a concentric circle. A circle with the same radius is called a circle.
The size of the circle
The size of a circle depends on its radius. The center of the circle determines the position of the circle. Because according to the definition of a circle, a circle is a geometric figure. When the radius of a line segment rotates around one end point on a plane, the trajectory perimeter of the other end point is called a circle. If the endpoint is determined and the radius is determined, then the circle is determined.
In classical geometry, the radius of a circle or circle is any line segment from its center to its periphery, and in more modern usage, it is also the length of any one of them.