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。

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