The Green's Theorem 格林公式
OK, so basically that tells you, you can still play tricks with Green's theorem when the region has holes in it.
负责任地告诉你们，当一个区域有个洞的时候,就可以这样巧妙地使用格林公式。
But, you can't use Green's theorem directly if the curve is not closed.
但是，如果曲线不是封闭的，不能直接使用格林公式。
Well, remember in the case of work we had Green's theorem.
请记得做功的例子，可以用格林公式的。
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