You can tell if you're at all experienced with it very easily, if you go--let's say to the year 900 B.C.

而如果你对此比较熟悉的话很容易看出来,如果你去--假定去公元前九百年

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It does represent the sum, in the sense that if i gave you four bucks and I gave you five bucks, I gave you effectively nine.

它表示的就是这两个矢量的和,好比是如果我给了你四美元,然后再给你五美元,我其实给了你九美元

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