7% 77% is class average and the standard deviation was 17% so you can see where things lie. 50% is a pass.

7是平均水平，标准偏差是%,这就是事情所在，50%就及格。

麻省理工公开课 - 固态化学导论课程节选

And when we're talking about the amplitude of the wave, we're talking about the deviation from that average level. So, if we define the average level as zero, you can have either a positive amplitude or a negative amplitude.

当我们讨论一个波的振幅时,我们说的是偏离平均位置的量,如果我们把平均位置,定义为零的话，那幅值不是,正的就是负的，有时候人们在。

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