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Math Help - y''=sin(2x) find and experssion

  1. #1
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    y''=sin(2x) find and experssion




    get confused with the wordy ones.......do I integrate this twice, then add coordinate values ?

    many thanks
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  2. #2
    A Plied Mathematician
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    You do integrate twice. In the process of so doing, you should obtain two arbitrary constants of integration. If you plug in those two points (which, incidentally, can be done while integrating, sometimes, to save effort), you will be able to determine what those arbitrary constants of integration are. Make sense? What do you get?
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  3. #3
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    when you start to talk about the constants it gets me sidelined...but heres what i did..?

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    oh almost forogt....does it have to be in radian?
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  5. #5
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    e^(i*pi)'s Avatar
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    Your second integration is incorrect - you're also integrating the +C from the first integration. You may also have a sign error on the first

    y' = -\dfrac{1}{2}\cos(2x) +c_1

    y = -\dfrac{1}{4}\sin(2x) + c_1x + c_2

    where c_1 \text{ and } c_2 are constants to be found


    edit: yes, it must be in radians. Nearly all trig calc is in radians as \dfrac{d}{dx} \sin(x) = \cos(x) (and all the others) work only in radians
    Last edited by e^(i*pi); May 25th 2011 at 07:50 AM. Reason: see post
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  6. #6
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    must i find c1 at y'
    or find c1 and c2 at y
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  7. #7
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    e^(i*pi)'s Avatar
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    The question says that "the function passes through" your two points - this would be y rather than y'.
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