This brought in their writing skills. After we talk about all of them, we will write the numbers down - now this is three and two more - before we even tell them the plus sign, you know,how to join things together."

VOA: standard.2010.08.10

And you can use mnemonics to try to keep these straight I see the T as sort of a plus sign.

你可以使用记忆术来记清它们,我将T看成是加号。

麻省理工公开课 - 固态化学导论课程节选

sa So we have 1 s a, and we're drawing this as having a positive amplitude, but since we have destructive interference we're going to draw 1 s b as having the opposite sign, so we have a plus and a minus in terms of signs.

我们有，我们把这画成一个正的振幅，但因为我们是相消干涉,我们把1sb画成相反的符号，所以我们有一正一负两个符号。

麻省理工公开课 - 化学原理课程节选