Until the Three Kingdoms period, Liu Hui put forward a scientific method to calculate π-secant, and approximated the circumference of a circle with the circumference inscribed by a regular polygon. Liu Hui calculated the circle inscribed with 96 polygons and got π=3. 14, and pointed out that the more sides inscribed with regular polygons, the more accurate the π value obtained.
On the basis of predecessors' achievements, Zu Chongzhi worked hard and calculated repeatedly, and found that π was between 3. 14 15926 and 3. 14 15927. The approximate value was obtained in the form of π fraction, which was used as reduction rate and ciphering rate, and the six decimal places were 3./kloc.
Pi (Pai) is the ratio of the circumference to the diameter of a circle, generally expressed by the Greek letter π, and it is a universal 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 expressed by the letter π (pronounced pài), which is a constant (approximately equal to 3. 14 1592654), indicating 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 1592654 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.
References:
Who's pi? The war between π and τ. [20 15-3- 18]
Definition of pi