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Math Help - Pretty simple question

  1. #1
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    Pretty simple question

    Although the topic is hard, this question is really simple...

    I have to calculate Laplace transformations for L{sint}, L{cost} and, L{-cost}. I did the first two, and for the last one I got that it equals:

    (-s)/(s^-1). Umm.. is this right? Is there supposed to be a negative in front of the a^2 value? (Rule from Laplace charts says L{cos(at)}= s/(s^2+a^2)..

    So.. yeah, just wondering if I'm messing this problem up, i've checked my work several times, but i thought you could pull a negative sign outside of a Laplace Transform (aka L{-f(t)}= -L{f(t)})

    Thanks ahead of time guys, hope this isn't a hard one

    I figured it out:

    For anyone who makes the same mistake as me by rare chance, you must solve for the Quantity of "-INT{e^-st*sint}". I solved for the normal int and distributed the negative into my equations so my answer was wrong.
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  2. #2
    MHF Contributor

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    Quote Originally Posted by drewkx152 View Post
    Although the topic is hard, this question is really simple...

    I have to calculate Laplace transformations for L{sint}, L{cost} and, L{-cost}. I did the first two, and for the last one I got that it equals:

    (-s)/(s^-1).
    You mean (-s)/(s^2- 1). What you wrote is -s^2!

    Umm.. is this right? Is there supposed to be a negative in front of the a^2 value? (Rule from Laplace charts says L{cos(at)}= s/(s^2+a^2)..

    So.. yeah, just wondering if I'm messing this problem up, i've checked my work several times, but i thought you could pull a negative sign outside of a Laplace Transform (aka L{-f(t)}= -L{f(t)})

    Thanks ahead of time guys, hope this isn't a hard one

    I figured it out:

    For anyone who makes the same mistake as me by rare chance, you must solve for the Quantity of "-INT{e^-st*sint}". I solved for the normal int and distributed the negative into my equations so my answer was wrong.
    Yes, exactly what I was going to say!
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