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Math Help - function problem.

  1. #1
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    function problem.

    How would I sovle...
    If f(g*x)) = x+5/x and g(x)= x+5, then f(x)=

    I thought it would be 1/x but their answer gives x/x-5. Can someone explain how they got that please?
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  2. #2
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    Quote Originally Posted by dnntau View Post
    How would I sovle...
    If f(g*x)) = x+5/x and g(x)= x+5, then f(x)=

    I thought it would be 1/x but their answer gives x/x-5. Can someone explain how they got that please?
    I'm assuming you meant f(g(x)) = (x+5)/x

    If f(x) = 1/x and g(x) = x+5 then f(g(x)) = 1/(x+5).

    You're asking for how they got their answer, but try to see why their answer is right. Maybe you'll see it better this way. Let g(x) = y. Then f(g(x)) = f(y) = y/(y-5) = (x+5)/(x+5-5) = (x+5)/x.

    I wouldn't use a systematic way to find f(x), just look at it and recognize that the numerator is g(x) and the denominator is g(x) - 5.
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  3. #3
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    That is what I meant. I see it now.
    Thanks so much.
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