Wu is equal to 3. 14 1592653 ... Pi is equal to 3. 14 1592653 in Greek letters, which is the ratio of circumference to diameter. It is an irrational number, that is, an infinite cycle decimal. In daily life, pi is usually expressed as 3. 14, which is used for approximate calculation. The fractional part 3. 14 1592653 is enough for general calculation. Even if engineers or physicists want to make more accurate calculations, they only need to take the values to a few hundred decimal places at best.

The origin of pi:

Before the Qin and Han dynasties, it was generally called "ancient rate" that "the diameter is three weeks" as π. Later, it was found that the error of ancient rate was too big, and pi should be "the diameter of the circle is one but more than that of Wednesday", but in the end it was not unified.

In the Three Kingdoms period, Liu Hui put forward a scientific method to calculate pi-"secant method", which approximated the circumference of a circle by the circumference of a regular polygon inscribed in the circle. On the basis of predecessors' achievements, Zu Chongzhi finally got the current pi after assiduous study and repeated calculus.

The ratio of the circumference to the diameter of a circle is a constant, usually called pi. It is usually represented by the Greek letter π. 1706, the Englishman Jones expressed pi for the first time. His symbols were not immediately adopted, but gradually became popular after Euler advocated them.

In ancient times, the value of π = 3 actually took a long time, as in Babylon, India and China. In the 2nd century BC, China recorded the Book of Changes in Shu Jing. Mathematicians in the Eastern Han Dynasty changed the π value to 3. 16.

It is because of Archimedes that the calculation of pi has a scientific basis. He specially wrote a paper "Measurement of Circle", and proved by geometric method that the ratio of pi to circle diameter is less than 22/7 and greater than 223/7 1. This is the first time in science that the upper and lower limits have been created to determine the approximate value.