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Math Help - Factoring, completeing square.

  1. #1
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    Factoring, completeing square.

    Hello and thank you all for the help.

    I am working on a problem and I am completely at a loss.

    this is the problem I am working on.

    (x-10)(x-2)=-20


    now I think this is what I am supposed to do,

    x^2-12x+20=-20
    +20 +20
    x^2-12x+40=0

    this is were I am lost.
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  2. #2
    Moo
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    Hello,

    What is the exact question ?

    The equation you got has no real solution ;-)

    I think they want you to complete the equation to got a perfect square.
    So use (a-b)=a-2ab+b, with a=x and 2ab=-12
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  3. #3
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    Sorry,
    The chapter we are in is Quadratic formula, Factoring and completing the square. and the question is Solve the each equation by the method of your choice.

    I can't however find an example of an equation of this type in the entire chapter. So I am pretty lost.
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  4. #4
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    I'll give that a try.
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  5. #5
    Moo
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    Ow !

    If you try to make a square :

    x-12x + ??? = ??

    With ??? a perfect square that will let you factorize x-12x+??? to a square

    So a=x
    2ab=12x, with b=???

    So b=6.

    So you must make appear 36 in the term.

    Which will give :

    x-12x+20=20 <=> x-12x+36=4 <=> (x-6)=4=2
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  6. #6
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    Great, I was so close but I just wasn't confident in what I was doing.

    Thanks so much for the help.
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  7. #7
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    Quote Originally Posted by EricS View Post
    Hello and thank you all for the help.

    I am working on a problem and I am completely at a loss.

    this is the problem I am working on.

    (x-10)(x-2)=-20


    now I think this is what I am supposed to do,

    x^2-12x+20=-20
    +20 +20
    x^2-12x+40=0

    this is were I am lost.
    Let a polynomial be Ax^2 + Bx + C = 0

    You have to use the quadratic equation: x = \frac{-B \pm \sqrt{B^2 - 4AC}}{2A}
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  8. #8
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    i hope you better use the distributive propety and then find its value.........
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