来自《耶鲁大学开放课程：金融理论 第3集 第3集》

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  P_Y times 2, and so she's spending 2 thirds
  P_Y乘以2 她将把收入的2/3
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  of it on X so therefore P_X times X^(D),
  花在X上 因此P_X乘以X^(D)
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  that's the amount of money she spends on X,
  就是她花在X上的钱
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  that's what she spends on X, has to be that,
  就是她花在X上的钱 就是这样
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  so X^(D) is that.
  X^(D)就是这个
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  And if I add these two, when I add them up I have to
  然后如果把这两个式子相加
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  get 2 1 = 3.
  就得到2+1=3
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  So I can just now solve this.
  于是我现在就可以解出它
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  Well, I can do a trick and pick one of my--either P_X
  我可以略施技巧 我假设P_X
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  or P_Y to be 1, so either one.
  或P_Y是1 随便哪个
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  I keep going back and forth.
  这个我反复做了很多遍了
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  It doesn't make any difference.
  意义不大