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Math Help - Need help integrating

  1. #1
    Junior Member
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    Need help integrating

    Hi all,

    I need help integrating:

    intg ((e^t)*cos(n*t))dt

    I have tried integrating by parts but it seemed like it just got more complicated. I know there is a theroem but i am not allowed to use it.

    Thanks in advance,
    ArTiCk
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  2. #2
    MHF Contributor Calculus26's Avatar
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    You actually integrate by parts twice and end up with a multiple of

    intg ((e^t)*cos(n*t))dt on both sides.

    Combine these ans solve

    In both cases let u = e^t to get started.

    Let me know if it works out
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by ArTiCK View Post
    Hi all,

    I need help integrating:

    intg ((e^t)*cos(n*t))dt

    I have tried integrating by parts but it seemed like it just got more complicated. I know there is a theroem but i am not allowed to use it.

    Thanks in advance,
    ArTiCk
    \int e^t \cos(nt)\; dt= \text{Re}\left\{ \int e^t e^{i n t}\; dt\right\}=\text{Re} \left\{\int e^{t(1+in)}\;dt\right\}

    CB
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  4. #4
    MHF Contributor Calculus26's Avatar
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    Heckuva lot easier than my approach
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