That translates into "Unfortunately, despite the most recent indicators that suggest the recovery may be in sight somewhat earlier than we were expecting only a few months ago, it will take far for the recovery to materialize in terms of significant improvement in the labor market,".

VOA: standard.2009.09.16

Mathematically, it's done by taking the expression for R and differentiating everything in sight that can be differentiated as vector t.

从数学上看是这样的,写出 R 的表达式,并对所有可以进行矢量微分的部分,对时间 t 求微商

耶鲁公开课 - 基础物理课程节选

Mathematically, it's done by taking the expression for R and differentiating everything in sight that can be differentiated as vector t.

从数学上看是这样的,写出 R 的表达式,并对所有可以进行矢量微分的部分,对时间 t 求微商

耶鲁公开课 - 基础物理课程节选