vertex of surface

例句：

1. 1. The vertexof the mountain is where the sun rises.
   山顶是太阳升起的地方。
2. 2. Thevertex of the triangle is the pointwhere all three sides meet.
   三角形的顶点是所有三条边交汇的地方。
3. 3. Thevertex of the parabola is thepoint where the curve touches the x-axis.
   抛物线的顶点是曲线与x轴接触的地方。