Pi is the ratio of the circumference to the diameter of a circle. Pi is expressed by the Greek letter π, which is a common mathematical constant in mathematics and physics. π is also equal to the ratio of the area of a circle to the square of its radius. Accurate calculation of geometric shapes such as circle perimeter, circle area and sphere volume is the key value. In the analysis, π can be strictly defined as the smallest positive real number x satisfying sin x = 0.

Pi is a constant (about 3. 14 1592654), which is an irrational number, that is, an infinite acyclic decimal. In daily life, pi is usually expressed as 3. 14, which is used for approximate calculation.

Calculation of China's ancient pi.

In 263 AD, China mathematician Liu Hui used the secant method to calculate pi. He first connected a regular hexagon from the circle and divided it step by step until the circle connected a regular hexagon 192.

He said, "If you cut carefully, you will lose very little. If you cut it again, you can't cut it. Then you will be surrounded and there will be no loss. " , contains the idea of seeking the limit. Liu Hui gave an approximate value of pi =3. 14 1024. After Liu Hui got pi = 3. 14, he checked this value with the diameter and volume of Jia Lianghu, a copper system made in the Han and Wang Mang dynasties in the gold armory, and found that the value of 3. 14 was still small.