If I gave you the location of a particle as a function of time, you can find the velocity by taking derivatives.

如果我给出物体的位移是时间的函数,你可以通过求导来得到速度

耶鲁公开课 - 基础物理课程节选

Initially, its location as a function of time is equal to i times x plus j times y.

初始时刻,它的位移作为时间的函数等于,i ? x + j ? y

耶鲁公开课 - 基础物理课程节选