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Homework Help: Simple functions question

  1. May 26, 2008 #1
    The functions f and g are defined by:

    f(x) = x^2 - 2x +3

    g(x) = k(x^2) + 1

    Given that gf(2) = 16, find the value of k

    My solution:

    f(2) = 3

    g(3) = 9k +1

    9k + 1 = 16

    k = 15/9

    However, the markscheme quotes "16=3k+1" therefore k =5.

    I am unable to understand how the markscheme came to this conclusion, please can someonebody help with this. The markscheme may have a mistake, which is what I am thinking!

  2. jcsd
  3. May 26, 2008 #2


    User Avatar

    Your solution looks fine to me. Looks like the key may have made a mistake of not squaring the 3 or something.
  4. May 26, 2008 #3


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    Homework Helper

    Yeah, it looks like the answer key didn't take into account the square.
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