There's a very natural quantity that you can call A + B.

有一个很自然的量可以记做 A + B
If you want to call something as A + B,

如果你想某个量称为 A + B
it means that I did A and then I did B.

它表示我先沿着 A 走然后是 B
But if I want to do it all in one shot,

但我如果想要一步完成
what is the equivalent step I should take?

那我应该用什么样的等价步骤呢
It's obvious that the bottom line of my two-day trip is this object C.

显然我两天的行程结果就是这个矢量 C
And we will call that A + B.

我们就称它为 A + B
It does represent the sum,

它表示的就是这两个矢量的和
in the sense that if i gave you four bucks

好比是如果我给了你四美元
and I gave you five bucks,

然后再给你五美元
I gave you effectively nine.

我其实给了你九美元
Here, we are not talking about a single number,

我们现在不是在讨论数字