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Math Help - Vertex!

  1. #1
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    Vertex!

    The function f(x) = x^2 - 18x + 83 achieves its minimum at (9,2). If g(x) = f(x-4)-3, where is the vertex of g(x)?

    This problem is driving me crazy!!!!

    Okay so far I've tried to do the shift thing. which I got: (13,-1)
    Then I tried to just plug it in as is and squared the equation which got me: (13,-4)

    Other answers I've tried: (5,-3) (13,2) (5,5) and so many others lols, on the record it said I've tried 28 times.

    Seriously, this seems like the EASIEST problem but I just can't get the right answer, please help.

    I won't even get full credit anymore but I realllyyyy want to know HOW to get the answer. Thank you~
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  2. #2
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    Re: Vertex!

    g(x)=(x-4)^2-18(x-4)+80

    Hence :

    g(x)=x^2-26x+168

    Vertex is given by :

    V\left(\frac{-b}{2a},\frac{-D}{4a}\right)

    where :

    a=1 , b=-26 , c=168 , D =b^2-4ac
    Thanks from Chuka
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  3. #3
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    Re: Vertex!

    hmmm, so the answer IS (13,-1)? X-x...Great, now i gotta tell the teacher

    [Update]
    WOW, fail...the answer IS (13,-1)... BUT turns out I had to put the answer in parentheses...maybe i should delete this thread.

    God I want to kill myself T_T;;
    Last edited by Chuka; May 10th 2012 at 02:32 AM.
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