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Math Help - Composite Function question

  1. #1
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    Composite Function question

    Hi,
    I'm a little confused over one of the questions I've been given for composite functions. I have the answer but I can't see how exactly we got there.
    The function given is q(p(x))

    Using for p:x=8/2x
    q:x=3x.

    So the solution given is 3(8/2x) = 24/2x = 12/x

    Question
    When we multiply 8/2x by the function of q which is 3x, why do we only mulitply the top line and not the bottom? I tried to do it 3(8/2x) = 24/6x = 12/3x = 4/x which is obviously incorrect.

    Thanks
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  2. #2
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    Re: Composite Function question

    Hi Davein,

    actually we do multiply the bottom by 1.

    3(8/2x) = (3/1) (8/2x) ; 3/1=3

    (3*8) / (1*2x) = 24/2x = 12/x


    p/s:
    a(x-y)=ax-ay
    a(x+y)=ax+ay
    a(xy)=axy
    a(x/y)=ax/y
    (x/y)^2=x^2/y^2


    cheers.......
    Thanks from Daveinthebigcity
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  3. #3
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    Re: Composite Function question

    Hi,
    Thanks for the reply. I obviously didn't learn rule 4 below. Thanks.
    a(x-y)=ax-ay
    a(x+y)=ax+ay
    a(xy)=axy
    a(x/y)=ax/y
    (x/y)^2=x^2/y^2
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