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Math Help - confused on factoring quadratics

  1. #1
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    Feb 2011
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    Pacific Northwest
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    confused on factoring quadratics

    Ok, this is super basic... I've been out of school for 5 years and decided to go back. I'm taking an online placement test to guesstimate where I should be and I'm stumped on one of the questions (a few, actually, but this one is really bugging me).

    The problem:
    (Solving polynomial equations by factoring)
    7. The solutions of x2 - 2x 24 = 24 are:
    A. 6,-4
    B. 8, -6
    C. 2, 48
    D. 20, 30
    E. 0,2


    I worked that out to
    x2 - 2x 48
    and then since

    -8 x 6 = -48
    and
    -8 + 6 = -2
    I figure the factors are
    (x-8)(x+6)
    so the answer is
    -8, 6

    ...right?

    BUT that's not a given choice... only 8, -6. Am I missing something simple that switches the signs, or should did the test writer screw up? I have absolutely no idea where I went wrong... it seems pretty simple.


    Help?
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  2. #2
    MHF Contributor
    Joined
    Dec 2009
    Posts
    3,120
    Thanks
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    Quote Originally Posted by JIBTEXHNKA View Post
    Ok, this is super basic... I've been out of school for 5 years and decided to go back. I'm taking an online placement test to guesstimate where I should be and I'm stumped on one of the questions (a few, actually, but this one is really bugging me).

    The problem:
    (Solving polynomial equations by factoring)
    7. The solutions of x2 - 2x 24 = 24 are:
    A. 6,-4
    B. 8, -6
    C. 2, 48
    D. 20, 30
    E. 0,2


    I worked that out to
    x2 - 2x 48
    and then since

    -8 x 6 = -48
    and
    -8 + 6 = -2
    I figure the factors are
    (x-8)(x+6)
    so the answer is
    -8, 6

    ...right? no!

    BUT that's not a given choice... only 8, -6. Am I missing something simple that switches the signs, or should did the test writer screw up? I have absolutely no idea where I went wrong... it seems pretty simple.


    Help?
    You have

    x^2-2x-48=0\Rightarrow\ (x-8)(x+6)=0

    and

    8-8=0

    6-6=0

    so the solutions are the values of x that make either factor zero, which are

    x=8,\;\;\;x=-6
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  3. #3
    Newbie
    Joined
    Feb 2011
    From
    Pacific Northwest
    Posts
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    OH RIGHT. Duh. ...Did I mention it's been a while?

    Thank you!
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