And then, what's the derivative in that direction?
那么，那个方向的导数是什么呢？
But, we can still ask, is there a derivative in every direction?
但我们仍想问，是否在每个方向上都有一个导数呢？
Well, it's actually the directional derivative in that direction.
它其实是那个方向的方向导数。
Well, it's actually the directional derivative in that direction.
它其实是那个方向的方向导数。
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