来自《耶鲁大学开放课程：基础物理 第16集 第16集》

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  It's just a number.
  最简单的数字运算
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  Divide that by x2 and that by x2
  分子两部分分别除以 x2
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  But I've got the sum of these two numbers in the bottom,
  但现在分母是个复数
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  and you can ask, "How do you do the division?"
  你就要问了 "这可怎么除啊"
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  So, the trick, always, when you run into this problem,
  应对这种问题的技巧就是
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  is to multiply the top and bottom by the complex conjugate of the bottom.
  分子分母同乘分母的共轭复数
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  Multiply it by x2-i·y2, top and bottom.
  上下都乘以 x2-i·y2
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  Then, something nice happens to the denominator,
  分母会变得很简单
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  because the denominator then becomes x2^2+y2^2,
  变为 x2^2+y2^2
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  which is an ordinary real number, nothing complex about that.
  是个实数 没什么复杂的
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  The numerator, you can open out the brackets.
  至于分子 把括号展开就行
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  I don't know if I want to do that;
  我觉得这一步我就不用讲解了吧