vertex angle

例句：

1. 1.The vertex of the triangle is at the right angle.
   三角形的顶点是直角。
2. 2.The vertex of the parabola is at the focus.
   抛物线的顶点在焦点。
3. 3. The vertex angles of a polygon are used to determine its shape.
   多边形的顶点角度用于确定其形状。