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Complex contour integral zero while containing a pole?

  1. Dec 4, 2013 #1
    [SOLVED] Complex contour integral zero while containing a pole?

    1. The problem statement, all variables and given/known data
    ##f(z) = \frac{1}{z^2 +2z +5} = \frac{1}{(z-z_1)(z-z_2)}##, where ##z_1= -1+2i## and ##z_2 = -1-2i##.

    Now, let z be parametrized as ##z(\theta)=Re^{i \theta}##, where ##\theta## can have values in the interval of ##[0,\pi]##. Furthermore, let ##R \rightarrow \infty## and ##a>0##. Show [tex] \lim_{R \to \infty} \int_{S_R} f(z) e^{iaz} dz = 0[/tex]

    3. The attempt at a solution

    My main problem with this, is that the upper half-plane contains a residue for ## f(z) e^{iaz}##, namely at ##z_1##, and thus the contour-integral can impossibly be zero...

    But on the other hand, I can see from the ML-inequality theorem that the sum of the integral should go towards zero when R goes towards infinity.. Help?
     
    Last edited: Dec 4, 2013
  2. jcsd
  3. Dec 4, 2013 #2
    edit nevermind, I just noticed that the parametrization is not a closed curve but rather a semi-circle. forget this thread.
     
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