A circle is a geometric figure, which refers to the set of all points on a plane with a constant distance from a fixed point. This given point is called the center of the circle. The distance as a fixed value is called the radius of a circle. When a line segment rotates once around one of its endpoints on a plane, the trajectory of its other endpoint is a circle. There are countless circles in diameter; A circle has countless axes of symmetry. The diameter of a circle is twice the radius, and the radius of a circle is half the diameter.
When drawing a circle with a compass, the point where the needle tip is located is called the center of the circle, which is generally represented by the letter O. The line segment connecting the center of the circle with any point on the circle is called the radius, which is generally represented by the letter R. The length of the radius is the distance between the two corners of the compass. The line segment passing through the center of the circle and with both ends on the circle is called the diameter, which is generally represented by the letter D.
A circle is a curved figure on a plane and an axisymmetric figure. Its axis of symmetry is the straight line where the diameter lies, and the circle has countless axes of symmetry.
A circle is a seemingly simple shape, but in fact it is very wonderful. The ancients first got the concept of circle from the sun and the moon on the fifteenth day of the lunar calendar. /kloc-Neanderthals 0/8000 years ago used to drill holes in animal teeth, gravel and stone beads, some of which were round. In the pottery age, many pottery were round. Round pottery is made by putting clay on a turntable.
When people start spinning, they make round stone spindles or ceramic spindles. The ancients also found it easier to roll when carrying logs. Later, when they were carrying heavy objects, they put some logs under big trees and stones and rolled them around, which was of course much more labor-saving than carrying them.
About 6000 years ago, Mesopotamia made the world's first wheel-a round board. About 4000 years ago, people fixed round boards under wooden frames, which was the original car.
You can make a circle, but you don't necessarily know its nature. The ancient Egyptians believed that the circle was a sacred figure given by God. It was not until more than two thousand years ago that China's Mozi (about 468- 376 BC) gave the definition of a circle: a circle, a circle of equal length. It means that a circle has a center and the length from the center to the circumference is equal. This definition is 100 years earlier than that of the Greek mathematician Euclid (about 330 BC-275 BC).
The ratio of the circumference to the diameter of any circle is a fixed number, which we call π(pai). It is an infinite acyclic decimal (irrational number), π = 3.141592 6535897 ... but in practical application, it usually only takes an approximate value, namely π≈3. 14. If the circumference is represented by c: C=πd or c = 2 π r.
When the Mesopotamians made the first wheel, they only knew that pi was 3. When Liu Hui annotated Nine Chapters Arithmetic in the Wei and Jin Dynasties in 263 AD, he found that "Three Circumferences and One Diameter" was only the ratio of the circumference to the diameter of a regular hexagon inscribed with a circle. He founded secant technology, and thought that when the number of sides inscribed with regular polygons in a circle increased infinitely, the circumference would be closer to the circumference of the circle.
He calculated the pi of a regular 3072 polygon inscribed in a circle = 3927/1250. Liu Hui applied the concept of limit to solving practical mathematical problems, which is also a great achievement in the history of mathematics in the world.
1500 years ago, Zu Chongzhi (AD 429-500) continued to calculate on the basis of previous calculations, and found that pi was between 3. 14 15926 and 3. 14 15927, which is the highest in the world.
In Europe, it was not until 1000 years later16th century that the Germans Otto (A.D. 1573) and Antoine Z got this value. Now with electronic computers, pi has been calculated to hundreds of millions of decimal places.