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Math Help - How to calculate g(f(x))

  1. #1
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    How to calculate g(f(x))

    I'm having a bit of trouble with this one:

    If f(x) = -5x+6 and g(x) = 4x+5, find g(f(x)).

    The answer is somehow -20x+29.

    Shouldn't it be -20x+30??

    Any help on how to solve this problem would be appreciated.
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  2. #2
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    Quote Originally Posted by softwareguy View Post
    I'm having a bit of trouble with this one:

    If f(x) = -5x+6 and g(x) = 4x+5, find g(f(x)).

    The answer is somehow -20x+29.

    Shouldn't it be -20x+30??

    Any help on how to solve this problem would be appreciated.
    g(f(x)) = g(-5x+6) = 4(-5x+6) +5 = .....
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  3. #3
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    g(f(x)) says g(-5x+6) so you plug that into your x for g.

    =4(-5x+6)+5

    6*4=24 + 5=29
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  4. #4
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    The composition says, where ever you see "x" in g(x), to put the function f(x):

    g(x) = 4x+5 \Rightarrow g(f(x)) = 4(-5x+6) + 5 \Rightarrow -20x+24+5 \Rightarrow -20x+29
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  5. #5
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    Quote Originally Posted by Debsta View Post
    g(f(x)) = g(-5x+6) = 4(-5x+6) +5 = .....
    f(x) = -5x+6
    g(x) = 4x+5
    g(f(x)) = g(-5x+6)
    = 4(-5x+6) + 5
    = -20x +24 +5
    = -20x + 29
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