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Composite Function

  1. Sep 14, 2009 #1
    1. The problem statement, all variables and given/known data
    If f(x) = x3+3x2+4x+5 and g(x)=5, then g(f(x)) = ?

    2. Relevant equations

    3. The attempt at a solution
    I don't know if I am correct.
    g(f(x)) =
    g(x3+3x2+4x+5)= 225?

    I plugged 5 into the equation. Am I right?
  2. jcsd
  3. Sep 14, 2009 #2
    If you plugged 5 into f(x), then you calculated f(5) = f(g(x)), since g(x) = 5. You want to find g(f(x)), which means plug f(x) into g(x).

    If you're having trouble, maybe ask yourself, what's g(1), g(10), g(1000)? Once you see a pattern, then g(f(x)) shouldn't be much harder.
  4. Sep 14, 2009 #3
    How do I plug a function into an integer? Would g(f(x)) just be 5?
  5. Sep 14, 2009 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    g(x) isn't an integer. It's called a constant function. And yep, g(f(x))=5.
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