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Homework Help: Need help Simplifying this Equation

  1. Nov 6, 2011 #1
    Hi, I've already worked out the question until part (a) but I don't understand how they go from (a) to (b) right at the bottom of the image.

    How did they change -s + i to s - i ?

    [PLAIN]http://img64.imageshack.us/img64/9366/unledrze.png [Broken]

    Thank you very much for your help.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 6, 2011 #2


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    What is -(s - i) ?
  4. Nov 7, 2011 #3
    Sorry to not have specified earlier.

    s is a constant (complex argument s for Laplace transform) and i is the imaginary number.

    Here's the solutions they provided. I though I should show you the bigger picture.

    [PLAIN]http://img36.imageshack.us/img36/7600/captureir.jpg [Broken]

    Thank you.
    Last edited by a moderator: May 5, 2017
  5. Nov 7, 2011 #4


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    That was not the point! SammyS was trying to get you to see that they went from -s+i to s- i by factoring out a "-1": -(s- i)= -s+ i.
  6. Nov 7, 2011 #5
    Ok thanks a lot hahahaha I feel so stupid.

    Actually I was panicking about the (-s + i)^2 to (s - i)^2 change at the denominator. Now I've just worked it out to be equal........

    Thanks a lot.
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