simple tangent

• 单切线

simple tangent的用法和样例：

例句

1. The graph of a concave function is always below its tangent.
   一个凹函数的图象总在它的切线的下方。
2. Both of approaching and returning movements are along the tangent of the circle.
   绕转之后移动方向为自南向北，也是沿圆周的切线运动。