正多边形如正三边形,正四边形,正六边形,正八边形其中称 a=面或边;b=垂綫或中垂綫;r=外容圓半径;c=2r=斜,或外容圆直径。此項实用做法,是以a边为基础,不用圆規来进行的。中国首先考虑这种正多边形实用做法,是建筑家李誡在他編輯的“营造法式”(1100年)內做到正四边形:a=100时,c=141; 正六边形:a=50时,b=87,c=100; 正八边形:a=5时,b=12,c=13。李誡是掌握着π=22/7,2~(1/2)=1.414,3~(1/3)==1.74的数值,所以假定,在正四边形 a:c= Positive polygons such as regular triangles, regular quadrilaterals, regular hexagons, regular octagons where a=face or edge; b=vertical or mid-perpendicular; r=external circle radius; c=2r=oblique, or external Round diameter. This practical approach is based on a side and does not require a compass. China first considered this practical approach to regular polygons. It was the constructionist Li Kui’s regular quadrilateral in his edited “Building Method” (1100): a=100, c=141; regular hexagon: a=50 , b=87, c=100; Positive octagon: a=5, b=12, c=13. Li Yong is holding the value of π=22/7,2~(1/2)=1.414,3~(1/3)==1.74, so assume that in the positive quadrilateral a:c=