Pi is the ratio of the circumference to the diameter of a circle.

Generally expressed by the Greek letter π, it is a universal mathematical constant in mathematics and physics. π is also equal to the ratio of the square of the area and radius of a circle, that is, π = the area of a circle ÷ radius 2 is the key value to accurately calculate the geometric shapes such as the circumference of a circle, the area of a circle, the volume of a sphere, etc. In the analysis, π can be strictly defined as the smallest positive number x satisfying sinx=0.

1665, the British mathematician john wallis published a mathematical monograph, in which he derived a formula and found that pi is equal to the product of infinite fractions. 20 15 scientists at the university of rochester found a formula with the same pi in the quantum mechanical calculation of hydrogen atomic energy level.

Characteristics of pi

π is an irrational number, that is, it cannot be expressed as the ratio of two integers, which was proved by German scientist johann heinrich lambert in 176 1. In 1882, Lin Deman proved that π is a transcendental number, that is, π cannot be the root of any integer coefficient polynomial. The transcendence of pi denies the possibility of turning a circle into a square, because all rulers can only draw algebraic numbers, and transcendental numbers are not algebraic numbers.

Set a floor paved with parallel equidistant wood grains, throw a needle with a length less than the distance between wood grains at will, and find the probability that the needle intersects with one of the wood grains. This is Buffon's needle throwing problem. 1777, Buffon solved the problem himself-the probability value is 1/π.