如果给定一条封闭曲线，那么求所做功的线积分为零。

If we have a closed curve then the line integral for work is just zero.

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如果段中存在间隙，则绘制一条假想线来使它封闭。

If there is a gap in a segment, draw an imaginary line to close it.

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如果段中存在间隙，则绘制一条假想线来使它封闭。

If there is a gap in a segment, draw an imaginary line to close it.

youdao