The advantage of introducing that guy is that if you like, I can now write an equation for the acceleration as a vector.

引入它的好处是,如果你愿意的话,我可以把加速度写成矢量形式

耶鲁公开课 - 基础物理课程节选

Well, the first thing you do is you write an equation.

嗯，第一点你要做的就是写一个方程。

麻省理工公开课 - 固态化学导论课程节选