设m 个正n 边形在平面上的一点接合，由于正n 边形的每一个 内角是 ，因此得 化简后得 mn-2m-2n=0 同顶角(angles at a point)：在一相同顶点上，全部角的总和等于360°。
双语例句
1
A white breakfast bar extends across the space at the point where the wall angles, heightening the separation between kitchen and lounge.
白色的早餐吧台顺着倾斜的墙壁延伸穿过整个空间，加强了厨房和休息室之间的分隔。
2
Pointanglesat outer corner and chisel edge corner are proposed to be used as the drill design parameters to determine the type uniquely and the relief Angle is used as a supplement parameter.