Jordan's lemma shows the value of the Integral

(1) |

(2) |

To derive the lemma, write

(3) | |||

(4) |

and define the Contour Integral

(5) |

(6) |

Now, if , choose an such that , so

(7) |

(8) |

(9) |

As long as , Jordan's lemma

(10) |

**References**

Arfken, G. *Mathematical Methods for Physicists, 3rd ed.* Orlando, FL: Academic Press, pp. 406-408, 1985.

© 1996-9

1999-05-25