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    the functions f and g are defined by f(x) = 3x-5 and g(x) = 3-2x

    evaluate
    c) fg(4)

    d) the composite function is defined by h=gf. find h(x)

    my working out:

    c) sub x with 4 and times f and g together?

    d) times g and f together?

    ahhhh :/
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    For C, sub x with 4 in g(x) then sub x for your answer from g(x) into f(x)
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    think of it as f(g(4)) rather than fg(4).

    So evaluate g(4) then use that answer as the x when evaluating f.

    Do the same for d.
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    For D, sub in f(x) as x in g(x)

    so

    3 - 2(3x - 5)
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    (Original post by Jabba1024)
    For D, sub in f(x) as x in g(x)

    so

    3 - 2(3x - 5)
    thank you so much for your help!

    another quick question :rolleyes:

    f(x) = 5x + 4

    find f^-1(x) and verify that the composite function f f ^-1(x) = x

    for the first part do you just sub -x in? for the second part have nooo idea
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    (Original post by boomboompow.)
    f(x) = 5x + 4

    find f^-1(x) and verify that the composite function f f ^-1(x) = x

    for the first part do you just sub -x in? for the second part have nooo idea
    A little trick: take everything "one step back."
    So make f(x) \rightarrow x, and every x \rightarrow f^{-1}(x).

    You'll then get:
    x=5f^{-1}(x)+4

    And then, for the first part, simply re-arrange this to make f^{-1}(x) the subject!

    It's probably best to post again once you've cracked the first part, before tackling the 2nd straight after ~
 
 
 
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