对圆内接正n多边形：

　　sin(π/n)=a(n)/(2R)=a(n)/D

　　a(n)=D*sin(π/n)

　　a(3)≈D*0.866x09或:x09a(3)≈D/1.155

　　a(4)≈D*0.707x09或:x09a(4)≈D/1.414

　　a(5)≈D*0.588x09或:x09a(5)≈D/1.7

　　a(6)≈D*0.500x09或:x09a(6)=D/2

　　a(7)≈D*0.434x09或:x09a(7)≈D/2.305

　　a(8)≈D*0.383x09或:x09a(8)≈D/2.613

　　a(9)≈D*0.342x09或:x09a(9)≈D/2.924

　　a(10)≈D*0.309x09或:x09a(10)≈D/3.236

　　a(11)≈D*0.282x09或:x09a(11)≈D/3.549

　　a(12)≈D*0.259x09或:x09a(12)≈D/3.864

　　a(13)≈D*0.239x09或:x09a(13)≈D/4.179

　　a(14)≈D*0.223x09或:x09a(14)≈D/4.494

　　a(15)≈D*0.208x09或:x09a(15)≈D/4.81

　　a(16)≈D*0.195x09或:x09a(16)≈D/5.126

　　a(17)≈D*0.184x09或:x09a(17)≈D/5.442

　　a(18)≈D*0.174x09或:x09a(18)≈D/5.759

　　a(19)≈D*0.165x09或:x09a(19)≈D/6.076

　　a(20)≈D*0.156x09或:x09a(20)≈D/6.392

　　a(21)≈D*0.149x09或:x09a(21)≈D/6.71

　　a(22)≈D*0.142x09或:x09a(22)≈D/7.027

　　a(23)≈D*0.136x09或:x09a(23)≈D/7.344

　　a(24)≈D*0.131x09或:x09a(24)≈D/7.661

　　-----------------------------------------------

　　D表示直径,

　　R表示半径,

　　a(n)表示圆内接正n多边形边长

　　*是乘号

　　/是除号