What is the definition of circle in middle school math

There are 2 definitions of circle in middle school math.

Definition 1: The set of points whose distance to a fixed point is equal to a fixed length is called a circle. This fixed point is called the center of the circle.

Definition 2: The points whose distance to the fixed point is equal to the fixed length are on the graph, and the points on the graph whose distance to the fixed point is equal to the fixed length.

In a plane, a moving point centered at a certain point and rotated by a distance of a certain length for one week forms a closed curve called a circle. A circle has an infinite number of axes of symmetry.

The set of points in the same plane whose distance to a fixed point is equal to a fixed length is called a circle. A circle can be represented as the set {M||MO|=r},The standard equation of a circle is (x - a) ? + (y - b) ? = r ? where o is the center of the circle and r is the radius.

Expanded:

The History of the Circle

The circle, a seemingly simple, is actually a very marvelous shape. Ancient people first got the concept of circle from the sun and the moon on the fifteenth day of the lunar calendar. Eighteen thousand years ago the cavemen used to drill holes in animal teeth, gravel and stone beads, and some of those holes resembled circles. By the time of the Pottery Age, many pottery vessels were round. Round pottery was made by placing clay on a turntable.

When people began spinning thread, round stone or pottery spindles were made again. Ancient people also discovered that it was less laborious to roll round pieces of wood when carrying them. Later, when they were carrying heavy loads, they put several pieces of round wood under large trees and rocks and rolled them around, which of course was much less strenuous than carrying them.

About 6,000 years ago, the Mesopotamians, made the world's first wheel, a round wooden disk. About 4,000 years ago, people fixed the round wooden disk under a wooden frame, which became the original car.

Baidu Encyclopedia-Circle