It depends what the problem is asking the question is, is it enough to find the components of a vector or do we have to find the equation of a line?
这都是根据题目要求而定的，有一个问题是，找出向量的分量就足够了吗？，还是说我们需要解出一条直线的方程？
So, now we can answer the initial question because vector OP, well, we just add up OA, AB, and BP.
现在我们可以回答最初的问题了，我们把OA, AB和BP加到一起。
Well, the question we have now is what is the area of this little piece of surface and what is its normal vector?
现在的问题是，曲面上这一小块儿的面积是什么，及其法向量是什么？
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