We can just find the angle using dot product So, how would we do that?
可以直接用点积来,找到这个角的大小，那么，怎么找呢？
These two vectors are perpendicular exactly when their dot product is zero.
当点乘的数量积为零时,这两个向量垂直。
这就是点积。
So, product rule is OK for taking the derivative of a dot product.
那么乘积法则对点乘求导没问题。
There is another way that you can find the dot product.
另一个定义,点积的方法。
Let us take a down-to-earth example of a dot product.
举一个点积的，现实例子。
The dot product, being the product of three scalars, is a scalar.
点积是三个标量的乘积，所以是个标量。
Remove any product labels or Department of Transportation (DOT) shipping hazard labels.
去掉产品标签或交通部(DOT)的运输危险品标志。
两个向量的点乘积。
两个向量的点乘积。
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