在一般高中平面几何課本里,規定圓的周長时,往往从一个固定的正多边形开始,繼續倍增这个正多边形的边数,便得到一系列正多边形,然后証明这一系列正多边形的周長有一个極限,那末就規定这样所得到的極限为圓的周長。就拿今年各高級中学所採用的課本来說,开始取的是正六边形,繼續倍增它的边数,便得 In general high school plane geometry textbooks, when defining the circumference of a circle, often starting from a fixed regular polygon, continue to multiply the number of sides of the regular polygon, to obtain a series of regular polygons, and then prove that there is a perimeter of the series of regular polygons. Ultimately, then it is stipulated that the limit thus obtained is the circumference of a circle. Take the textbooks used in this year’s senior high schools, starting with a regular hexagon and continuing to multiply its number of sides.