The circle is a seemingly simple, but actually wonderful circle.
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 beads, some of which were round.
Later, 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 stones or ceramic cocoons.
The ancients also found that rolling logs was more economical. 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 2,000 years ago that China's Mozi (about 468- 376 BC) defined the circle: "One China has the same 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).
Pi, the ratio of circumference to diameter, is a very strange number.
The Book of Weekly Calculations says that "the diameter is three times a week", and pi is considered to be 3, which is only an approximate value. When the Mesopotamians made the first wheel, they only knew that pi was 3.
In 263 AD, Liu Hui of Wei and Jin Dynasties annotated Nine Chapters of Arithmetic. He found that "the diameter is three times that of a week" is just the ratio of the circumference to the diameter of a regular hexagon inscribed in a circle. He founded secant technology, and thought that when the number of inscribed sides of a circle increased infinitely, the circumference was closer to the circumference of a 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.
Zu Chongzhi (AD 429-500) continued to calculate on the basis of predecessors' calculations, and found that pi was between 3. 14 15926 and 3. 14 15927, which was the earliest numerical value accurate to seven decimal places in the world. He also used two decimal values to express pi: 22/7 is called about.
In Europe, it was not until 1000 years later16th century that the Germans Otto (A.D. 1573) and Antoine Z got this value.
Now that there is an electronic computer, pi has been calculated to more than 10 million after the decimal point.
The fourth grade elementary school mathematics simple handwritten newspaper content II
Intersection and vertical knowledge points
1, the concepts of intersection and verticality. When two straight lines intersect at right angles, they are perpendicular to each other. (perpendicular to each other: straight line OA is perpendicular to straight line OB, and straight line OB is perpendicular to straight line OA) The intersection of these two straight lines is called vertical foot. The fact that two straight lines are perpendicular to each other illustrates the positional relationship between the two straight lines: they must intersect and intersect at right angles. )
2. Draw a vertical line:
(1) The method of drawing a vertical line through a point on a straight line.
Overlap one right-angle side of the triangle ruler with this straight line, the vertex of the right angle is the vertical foot, and draw a straight line along the other right-angle side, which is the perpendicular of the previous straight line. Pay attention to make the right-angle vertex of the triangular ruler coincide with the given point.
(2) the method of drawing vertical lines outside the straight line.
Overlap one right-angle side of the triangle ruler with this straight line, let the other right-angle side of the triangle ruler pass through this known point, and draw a straight line along the other right-angle side of the triangle ruler, which is the perpendicular of the previous straight line. Note that when drawing, you usually hold a triangular ruler in your left hand and draw lines in your right hand. Draw a vertical line through a point outside the line, and the other right-angled side of the triangular ruler must pass through a given point.