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Math Help - Substitution problem

  1. #1
    Newbie
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    Oct 2010
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    Substitution problem

    Hi, I have to solve

    -(y+x)^2/(1+(y+x)^2)=dy/dx

    using the substitution u=y+x. It isn't necessary to explicitly for y in terms of x.

    How do I go about doing this? Do I need to use partials when converting to du/dx?

    Cheers,
    Ben
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  2. #2
    A Plied Mathematician
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    Do I need to use partials...
    Nope. Just set u = y + x. Then u' = y' + 1. It follows that u' - 1 = y'. Substitute into your DE, and off you go.
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