at a tangent

• adv. 沿着切线的方向(突然离开正常程序)

at a tangent的用法和样例：

例句

1. It's not easy to follow her think because she's always go off at a tangent.
   要跟上她的思路并非易事，因为她老是突然扯到题外去。
2. The teacher was telling us about the poet's life, when he went off at a tangent and started talking about his war experiences.
   老师在给我们讲述诗人生平故事的时候，突然把话题一转，讲开他自己的战争经历来了。