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Homework Help: Exp(i*k-a)*x=0 for x= inf

  1. Oct 2, 2012 #1
    1. The problem statement, all variables and given/known data
    In a solutions manual I read exp(i*k-a)*x=0 when x= inf. I don't see how this happens.

    2. Relevant equations

    3. The attempt at a solution
    Is there a procedure for dealing with this like l'Hospital's rule?
    Like if I distribute the x for exp(i*k*x-a*x) then substitute inf, and get exp(inf-inf).
  2. jcsd
  3. Oct 2, 2012 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    Assuming throughout that k is real, the statement is true if a > 0, false if a ≤ 0. For the case a > 0 we just have "exponential damping" of the form exp(-a*x)*f(x), where f(x) = exp(i*k*x) remains bounded.

  4. Oct 2, 2012 #3
    Yes, I'm sorry. a is positive and real. As is k
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