切线的英文：
tangent

参考例句：

U Tangent
U向切线

V Tangent
V向切线

Project Tangent
曲线切线调整

Flip Tangent
反转切线

Selected Tangents
已选择的切线

The direction is tangent to the trajectory.
方向就是轨道的切线方向。

asyzygetic bitangents(of a quartic)
不合冲双切线(四次曲线的)

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。

Arrowheads on the lines indicate the direction in which the tangent is to be drawn
电力线上的箭头表示所要画的切线方向。

A perpendicular,especially a perpendicular to a line tangent to a plane curve or to a plane tangent to a space curve.
正交一条垂直线，尤指一条相对一条平面曲线的切线垂直线或一条相对一条空间曲线的平面切线垂直线

tangent是什么意思：
n. 正切；直线区间；突兀的转向；突然转移话题

The direction is tangent to the trajectory.
方向就是轨道的切线方向。

The tangent is a relatively important concept in trigonometry.

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。

Arrowheads on the lines indicate the direction in which the tangent is to be drawn
电力线上的箭头表示所要画的切线方向。

Don't fly off at a tangent, we are talking about the money problem.
不要扯别的，我们谈的是那笔钱的问题。