tangent between curves

例句：

1. 1.The circle's tangent at the center divides it into two equal halves.
   圆的切线在圆心将圆分成两个相等的部分。
2. 2. The straight line from A to B is the shortest distance between them.
   从A到B的直线是它们之间最短的距离。
3. 3. The perpendicular line divides the plane into two parallel sides.
   垂直线将平面分成两个平行边。