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Math Help - Differential Equation help!

  1. #1
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    Differential Equation help!

    I'm having a real hard time solving this:

    dy/dx -5y = 20cos(5x)

    I have tried mixing everything around and I can't seem to remember how to get y and dy, x and dx on separate sides of the equation. I know I am missing one step!

    Any help would be great!
    Cheers.
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by falconed View Post
    I'm having a real hard time solving this:

    dy/dx -5y = 20cos(5x)

    I have tried mixing everything around and I can't seem to remember how to get y and dy, x and dx on separate sides of the equation. I know I am missing one step!

    Any help would be great!
    Cheers.
    Do you know anything about the integrating factor? This is a scenario where it's applicable. For a little info on the integrating factor, see post #2 of my differential equations tutorial.

    --Chris
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  3. #3
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    Quote Originally Posted by Chris L T521 View Post
    Do you know anything about the integrating factor? This is a scenario where it's applicable. For a little info on the integrating factor, see post #2 of my differential equations tutorial.

    --Chris
    Yeah I do but the example I have in my lecture notes is quite different.

    Would I(x) here be e^(5x) or e^(-5x)? Does it matter?
    Last edited by falconed; October 21st 2008 at 11:57 PM.
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  4. #4
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by falconed View Post
    Yeah I do but the example I have in my lecture notes is quite different.

    Would I(x) here be e^(5x) or e^(-5x)? Does it matter?
    It does matter. The integrating factor would be \varrho(x)=e^{\int -5\,dx}=e^{-5x}

    --Chris
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