"tangent" in Chinese (Simplified)
切线离题的话
Definition
只在一个点上接触曲线(不交叉)的直线。口语中，也指谈话时突然说到其他话题。
Usage Notes (Chinese (Simplified))
数学中为正式用语，表示精确的“切线”；口语中“go off on a tangent”常指话题离题扩展，不要和“topic”本意混淆。
Examples
A tangent touches the circle at only one point.
**切线**只在一个点上接触圆。
He loves to talk about math, especially about the tangent of a curve.
他喜欢谈论数学，尤其是曲线的**切线**。
Try not to go off on a tangent during your presentation.
演讲时尽量不要**跑题**。
We were talking about movies, but then she went off on a tangent about her cat.
我们在聊电影，然后她突然**说到**她的猫。
The math problem asks for where the line is tangent to the parabola.
这道数学题问直线在哪一点与抛物线**相切**。
Sorry, I went on a tangent—let's get back to the main point.
不好意思，我刚刚**扯远了**——我们回到正题吧。