如果我们必须计算线积分，就必须通过寻找一个参数，并建立起一切。

If we have to compute a line integral, we have to do it by finding a parameter and setting up everything.

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我们用一个参数来表示所有的项，最后得到一个通常的积分。

We express everything in terms of a single parameter, and that will give us a usual single integral.

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如果无法对曲线参数化，那么就很难计算线积分了。

If you cannot parameterize the curve then it is really, really hard to evaluate the line integral.

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