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Math Help - functions

  1. #1
    Master Of Puppets
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    [SOLVED] functions

    The function f has the property that f(x)+f(y)= (x+y)f(xy) for all non-zero real numbers x and y . A possible rule for f is

    A. f(x)=2x

    B. f(x)=5-2x

    C. f(x) = \frac{1}{x}

    D. f(x)= e^x

    E. f(x)=\ln x

    I can expand every option out. But I'm having a lazy day. Is there an easier way?
    Last edited by pickslides; April 7th 2010 at 05:11 PM.
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  2. #2
    Master Of Puppets
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    C. is the answer. Just lazy I am.
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  3. #3
    Super Member Bacterius's Avatar
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    I don't think so. I've been thinking but I can't express the property in natural terms that do not require expanding each function to see if it matches.
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