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Homework Help: Dirac delta integrals

  1. Nov 6, 2013 #1
    1. The problem statement, all variables and given/known data
    This is just an example, not a specific problem.

    So if I have ∫σ(sinx), for example, and my limits of integration are, for example, 1 to 10, what I need to do to solve that is to find a value of x that would make the argument of the delta function 0. So for sinx, 0 makes the argument 0. But since it's outside of the limits of integration, the integral would be 0, correct? What if my limits of integration are 1 to 10, and I input pi as the argument for sine? I'm unsure of what to input in for the x, because I have 1 to 10 in the limits of integration, so does that mean I use degrees instead of radians?

    Or for that one do I use the formula which is σf(x) = Ʃ σ(x-xi)/|f'(xi)|?
    If f(xi) = 0 and f'(xi) does not = 0.

    Using that formula, I still have to decide whether to use radians as my x (pi) or degrees (180).

    Last edited: Nov 6, 2013
  2. jcsd
  3. Nov 6, 2013 #2


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    Science Advisor
    Gold Member

    Correct! And for your next question: you should always use radians; otherwise it is the angle*pi/180.
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