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Math Help - Completing the square in quadratics of the form x^2 + bx + c

  1. #16
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    Re: Completing the square in quadratics of the form x^2 + bx + c

    Quote Originally Posted by Siron View Post
    Can you be more clear about your question? We've found the complete square of x^2-8x-5 which is (x-4)^2-21.
    Where are you stuck? What do you not understand? ...
    I thought the completed square was the first part that was worked out.

    x^2 - 8x - 5

    (x - 4)^2 - 16 without the - 5 being added, why am I wrong?
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  2. #17
    MHF Contributor Siron's Avatar
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    Re: Completing the square in quadratics of the form x^2 + bx + c

    Completing the square is a technique for converting a quadratic polynomial of the form ax^2+bx+c into the form a(x-p)^2+q where p,q are constants.
    So that's what we've done here and notice (x-4)^2-16=x^2-8x+16-16=x^2-8x.

    Does this answers your questions? ...

    If you want to have a confirmation take a look here:
    http://www.wolframalpha.com/input/?i=complete+the+square+of+x^2-8x-5
    Last edited by Siron; August 9th 2011 at 03:26 PM.
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