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Math Help - Null factor Law

  1. #1
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    Null factor Law

    Factorise and solve:

    x^2 + 6x - 72 = 0
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  2. #2
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    this is a relatively easy factorization...

    (x+12)(x-6)=0

    x=-12, 6

    Why did you have a problem with it?
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  3. #3
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    Smile

    Just wasn't thinking right. Though don't get me wrong, usually I am not that good at math also. So, I'm prone to mistakes.
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  4. #4
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    Dec 2007
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    Here is the whole process so you can study it

    x^2+6x-72=0

    We try find the factos adding to 6

    1(-72)=-72 -71
    2(-36)=-72 -34
    3(-24)=-72 -21
    4(-18)=-72 -14
    6(-12)=-72 -6
    12(-6)=-72 6

    Now we have to re-write our equation

    x^2+12x-6x-72=0
    x(x+12)-6(x+12)=0
    (x-6)(x+12)=0

    Then:
    x-6=0
    x=6

    or
    x+12=0
    x=-12
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