So, in both cases, we need the vector field to be defined not only, I mean, the left hand side makes sense if a vector field is just defined on the curve because it's just a line integral on c.
了解这两种表述后，我们不仅需要向量场，就是左边这里，这是曲线c上的线积分，向量场在曲线上有定义。
Let's say that we had the same c, but now the vector field.
假设c还是一样的，但现在的向量场变为。
At the forefront of the pioneers in the field was the Greek mathematician and philosopher Claudius Ptolemaeus (c. AD 90 ?168), more popularly known to history as Ptolemy.
这一领域的先驱中最早的是希腊数学家和哲学家克劳迪•托勒密(约公元90年～168年)，历史上多称他托勒密。
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