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Homework Help: Inverse Functions

  1. Apr 23, 2013 #1
    1. The problem statement, all variables and given/known data

    5. (a) The functions f and g are defined by
    f : x|→ 2x + ln3 (x is a real number)
    g : x|→ e^3x (x is a real number)

    i) Find f^-1(x) and g^-1(x) and state their domain of definition

    ii) Show that f^-1 f = f f^-1 = x (x is a real number)

    iii) Find the composite function gf x( )and state the range.

    2. Relevant equations

    3. The attempt at a solution

    So i worked out the inverse for each.

    f^-1(x) = 1/2(x-ln3)
    g^-1(x) = 1/3(lnx)

    But for part two I'm not sure what this means, does it mean that i should sub my inverse fucntion into my original function and then vice versa?

    Also when i double checked my answer, it has log's in place of my ln's. Was i meant to use log instead of ln? :S
  2. jcsd
  3. Apr 23, 2013 #2


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    Science Advisor
    Homework Helper

    Yes. That's exactly what it means. You should get x for both answers, that's the identity function. And here 'log' and 'ln' mean the same thing. 'log' can be used if you are talking about any base. If you want to be specific then you need to indicate the base, i.e. ##log_2##. 'ln' is ##log_e##.
  4. Apr 23, 2013 #3
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