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Homework Help: If f(x)=2x^2 + 1 and g(x) = x -1, find f+g, composition of f&g, and their domains.

  1. Jun 27, 2010 #1
    1. The problem statement, all variables and given/known data

    posted in title

    2. Relevant equations

    none

    3. The attempt at a solution
    f+g would be

    (2x^2+1) + (x-1) = 2x^2 + x so the domain for f+g is all real numbers but i dont know how to find the one for the composite. i am still confused as to what a composite function is, please help me!!! thank you!
     
  2. jcsd
  3. Jun 27, 2010 #2

    rock.freak667

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    Homework Helper

    Re: If f(x)=2x^2 + 1 and g(x) = x -1, find f+g, composition of f&g, and their domains

    composition of f&g is nothing but f o g which is the same as fg or f(g(x)).

    So take the entire g(x) and put it wherever you see 'x' in f.
     
  4. Jun 27, 2010 #3
    Re: If f(x)=2x^2 + 1 and g(x) = x -1, find f+g, composition of f&g, and their domains

    the composite is simply g then? or is it f(x) multiplied by g(x)?
     
  5. Jun 27, 2010 #4

    danago

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    Gold Member

    Re: If f(x)=2x^2 + 1 and g(x) = x -1, find f+g, composition of f&g, and their domains

    As rock.freak said, it is f(g(x)), not g(x). 'x' is the input to g and then the output g(x) becomes the input to f. It is different to multiplying.

    As an example: If g(x)=x+x^2 and f(x)=2x, then the composition gf(x) = 2x + (2x)^2
     
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