构造向量，利用向量内积进行求解，为函数最值问题的解决，开辟了一种新的思路和方法。
But the author explored a new way to solve this problem, which is to wake up vector and make us of the internal product to go on solution.
例如，在某些情况下，如果已知向量场与曲线相切，或者内积是一个常数等等，那么结果将会很简单。
And, in some cases, for example, if you know that the vector field is tangent to the curve or if a dot product is constant or things like that then that might actually give you a very easy answer.
这门课我们首先学习的概念是向量，以及怎样做向量的内积。
So, the first things that we learned about in this class were vectors, and how to do dot-product of vectors.
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