Now, how do we get this unit vector?
那我们怎么得到这单位矢量呢？
它不是单位向量。
It's the unit vector in the vertical direction.
即竖直方向的单位向量。
So, that means this actually should be the unit vector.
这意味着这一项就是单位向量。
How to choose appropriate unit vector to establish new inequalities.
如何选择合适的单位向量来创建新的不等式。
Remember that was the vector field that looked like a rotation at the unit speed.
我们记得，这是个以单位速度旋转的向量场。
And that is, in general, not a unit normal vector.
这通常不是一个单位法向量。
Now, let's multiply that by the unit normal vector.
现在用单位法向量乘以那个。
Now, let's multiply that by the unit normal vector.
现在用单位法向量乘以那个。
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