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Homework Help: Fourier transform time shift

  1. Jul 8, 2006 #1
    I am given this signal:
    x(t) = sin(4(t-1))
    and I need to find X(jw), i.e. it's FT, so I am confused whether I shift by 1 or by 4, in other words whether I multiply F{sin(4t)} by e^(4jw) or by e^(1jw)

    which one is it? I am thinking it's 4jw.... is it right?
     
  2. jcsd
  3. Jul 8, 2006 #2

    HallsofIvy

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    Science Advisor

    Aarg! Those engineers and their jmaginary numbers!

    I hope you will bear with me as I use "i" rather than "j". I just can't force myself to that heresy.

    sin(4(t-1))= sin(4t- 4). Looks to me like you need to shift by 4.
     
  4. Jul 9, 2006 #3
    :tongue2: :biggrin:

    thanks
     
  5. Jul 9, 2006 #4
    a bit off topic

    perhaps i should have started a different thread, but since HallsofIvy has mentioned, i couldn't help but ask: is there any tiniest difference between i and j, i.e. are we, engineers, underestimate imaginary numbers in some way?
    It always comes up and i just would like to satisfy my curiosity.:bugeye:
     
  6. Nov 19, 2009 #5
    Mr EvLer,

    There is no big deal in taking j instead of i for imaginary numbers. For engineers, 'i' represents current. To avoid confusion engineers take 'j' for imaginary part.
     
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