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F of g, simple

  1. Jun 11, 2010 #1
    1. The problem statement, all variables and given/known data

    (f of g)

    f(x)= sqrt/x

    g(x) = x+1

    2. Relevant equations

    (f of g)(3)

    3. The attempt at a solution

    sqrt/3 (4) = 4(sqrt/3) (incorrect)

    Correct answer is 2 but I don't see how?
  2. jcsd
  3. Jun 11, 2010 #2


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    Homework Helper

    f(x)=sqrt/x has no sense. Is not it f(x)= sqrt(x)?

  4. Jun 11, 2010 #3
    You are absolutely correct, sorry, I see now that I put it in improperly. I've made it harder^2
  5. Jun 11, 2010 #4
    You are doing in your working (f * g), not (f of g). In the latter, you pass the result of g to f.
  6. Jun 12, 2010 #5
    I'm just not seeing what you are saying for some reason, if (x)=3 don't I substitute every (x) with 3?
  7. Jun 12, 2010 #6


    Staff: Mentor

    No, not at all. To evaluate f(g(3)) you need to evaluate g(3), and then use that number in f.

    For example, if g(3) = 5 -- I'm just making up numbers here -- then you would evaluate f(5). That would be f(g(3)).
  8. Jun 12, 2010 #7
    OH!!! I see! Thank you very much.
  9. Jun 12, 2010 #8


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    Science Advisor

    I would say "yes, you do", but that [itex]fog(x)= f(g(x))[/itex] only has one x!
    Last edited by a moderator: Jun 13, 2010
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