That quantity in parenthesis, I have a mass which is a positive number. Something raised Something raised to the fourth power has got to be positive.

顺便说一句,质量这个量是个正数,四次方的值,肯定是正数。

麻省理工公开课 - 固态化学导论课程节选

Something raised to the second power has got to be positive.

二次方的东西,也一定是正数。

麻省理工公开课 - 固态化学导论课程节选