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Fourier transform

  1. Oct 26, 2004 #1
    hi ,

    the question is to find the fourier transform of the following eqn without using integration

    d(t)= [c(-1.5t)]exp(jwat)

    c(t)= Ao + E(Sumation)An*cos(nwot) + Bn sin(nwot) [fourier series formula]

    I knwo to find the FT of the above fourier series. But why is exp(jwat)
    the frequency shift and why shud we shift by wa.

  2. jcsd
  3. Oct 26, 2004 #2


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    Science Advisor
    Homework Helper

    Please don't cross/double post.

    I'm assuming that:
    since you're a phyicist.

    Then if you apply the euler equation:
    [tex]e^{j\theta}=\cos \theta + j \sin \theta[/tex]

    you should see how the exponent affects the frequency.
  4. Oct 26, 2004 #3
    Sorry for the double post.

    1.Thanks but I take the FT of c(t) first and then I shift all the impulse functions by wa.
    can someone please explain why as i dont understand why this is done this way.

    2.Also I thought that the Integral of an impulse function is 1, but here its says that the integral of a impulse function is a unit step function.

  5. Oct 26, 2004 #4
    I mean I read in my notes that the integral of a impulse function is a unit step function
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