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Homework Help: BASIC LAPLACE - Unit Step.

  1. Apr 18, 2010 #1
    1. The problem statement, all variables and given/known data

    Find the Laplace transform of cos(t)h(t)
    if the LT of h(t) (unit step) is 1/s


    2. Relevant equations

    ---

    3. The attempt at a solution

    Since the unit step isn't shifting anything anywhere, can I just treat it as 1? Seems too simple, haha. Any ideas? thanks.
     
  2. jcsd
  3. Apr 19, 2010 #2
    Here's a similar one - Find the LT of (e^-3t + 2)h(t)
    with h(t) the same as before.

    Would the h(t) just act as a 'turn on' in these cases?
     
  4. Apr 19, 2010 #3

    vela

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    Yes, and as you noted, it's superfluous with the usual Laplace transform. If you are using the double-sided transform, the presence of the step function would effectively give you the one-sided transform.
     
  5. Apr 19, 2010 #4
    Ok, thanks.

    So would the above LT simply be-

    1/(s+3) + 2/s

    ?
     
  6. Apr 19, 2010 #5

    vela

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    Yup.
     
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