圆周率是一个在数学及物理学领域中普遍存在的常数,人们通常用π来表示。它是一个无理数,即是一个无限不循环小数。它定义为圆周长与直径之比,或者圆面积与半径平方之比,是精确计算圆周长、圆面积、球体积等几何形状的关键 Pi is a ubiquitous constant in mathematics and physics, and people usually use π to represent it. It is an irrational number, that is an infinite non-recurring decimal. It is defined as the ratio of the circumference to the diameter, or the ratio of the area of ​​the circle to the square of the radius, which is the key to accurately calculate the geometry of the circumference, circle area, sphere volume, etc.