你若称此为正号，你若想要一个负号，你们知道的，相反方向的速度。

If you call this plus, then if you get a minus sign, you know that the velocity is in the opposite direction.

youdao

要找出时间来考虑一下，一天中做了什么，是正号还是负号。

To find the time to consider, do in a day, plus or minus sign.

youdao

要找出时间来考虑一下，一天中作了什么，是正号还是负号，假如是正号很好。

To find the time to consider, what did during the day, it is plus or minus sign, if is a very good plus.

youdao

Sometimes you see this written when you see p orbitals, one is written as plus, one is written in minus.

有时候你们看ｐ轨道时会看到，一个写成正号一个写成负号。

麻省理工公开课 - 化学原理课程节选