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Math Help - Derivative and differential equation problem?

  1. #1
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    Derivative and differential equation problem?

    Is my answer for this: Derivative and differential equation problem?-capture2.jpgright? I'm having a lot of trouble with this because of the "yy'" part. I know obviously what y' means but yy' confuses things. Any help? Could someone walk me through this? :/
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  2. #2
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    Re: Derivative and differential equation problem?

    $y y' - e^x=0$

    $y \dfrac{dy}{dx} = e^x$

    $y dy = e^x dx$

    what's so confusing about that?
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  3. #3
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    Re: Derivative and differential equation problem?

    Quote Originally Posted by romsek View Post
    $y y' - e^x=0$

    $y \dfrac{dy}{dx} = e^x$

    $y dy = e^x dx$

    what's so confusing about that?
    Oh okay. So when I plug in (0,4) I get c=7? But I don't know how that relates to any of the options :/ I'm feeling really stupid right now. This question is just going over my head for some reason..
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    Re: Derivative and differential equation problem?

    From romsek's y\,dy=e^x\,dx, when you integrate both sides you should get \frac{1}{2}y^2=e^x+C, and then, yes, C=7. So you have \frac{1}{2}y^2=e^x+7. Now multiply both sides by 2.

    - Hollywood
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    Re: Derivative and differential equation problem?

    Quote Originally Posted by hollywood View Post
    From romsek's y\,dy=e^x\,dx, when you integrate both sides you should get \frac{1}{2}y^2=e^x+C, and then, yes, C=7. So you have \frac{1}{2}y^2=e^x+7. Now multiply both sides by 2.

    - Hollywood
    Oh! Thank you! so y^2=2e^x+14
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