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Math Help - Composite Functions

  1. #1
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    Composite Functions

    For this question: find gof:
    f: R ---> R and g: R ---> R given by f(x) = 2x -5 and g(x) = 5x +2

    I've done my working out and would like to know if this is correct.

    (fog)(x) = f(5x+2)
    (fog)(x) = 2(5x+2)-5
    (fog)(x) = 10x+4-5
    (fog)(x) = 10x-1

    Is that all I need to do for this question and is what I've done right?
    The R's obviously mean real numbers.
    Last edited by brumby_3; April 25th 2010 at 09:06 PM. Reason: ooops I just realised I posted this in the wrong section!!!
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  2. #2
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    Hello, brumby_3!

    You found the wrong composite . . .



    f\!:\! R \to R\:\text{ and }\:g\!:\! R \to R

    . . given by: . \begin{array}{ccc}f(x)& =&2x -5 \\g(x) &= &5x +2\end{array}

    Find {\color{red}g\circ f}

    g\circ f \;=\;g(f(x))

    . . . . =\;g(2x-5)

    . . . . =\;5(2x-5) + 2

    . . . . =\;10x-25+2

    . . . . =\; 10x - 23

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