来自《耶鲁大学开放课程：基础物理 第7集 第7集》

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  I think for our purpose,
  我想对于我们的目标
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  even if you took a single cone
  即使你拿一个圆锥
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  and you cut it at some angle,
  你倾斜某个角度再去切割它
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  that would be an ellipse.
  会得到一个椭圆
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  That's why the Greeks were studying this.
  这是为什么古希腊人研究这个
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  But you need a second cone for other things.
  但是你以后会需要第二个圆锥
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  But for now, if you slice a cone parallel to the base,
  但是现在 如果你平行于底面去切圆锥
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  you'll get a circle;
  你会得到一个圆
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  at an angle, you'll get the ellipse.
  有一个角度的话 你得到椭圆
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  So, that's the first statement.
  这是第一定律
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  Second statement is the following:
  第二定律是这样说的
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  If you pick one planet and it's there today,
  如果你选一个行星 它今天在这里