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Math Help - Factor each of the following

  1. #1
    LOL
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    Factor each of the following

    x2+9x+20

    s2-100

    t2-3t-28

    36m2-121

    How do you factor
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  2. #2
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    Quote Originally Posted by LOL View Post
    x2+9x+20

    s2-100

    t2-3t-28

    36m2-121

    How do you factor
    Factoring Quadratics: The Simple Case
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  3. #3
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    Quote Originally Posted by LOL View Post
    x2+9x+20

    s2-100

    t2-3t-28

    36m2-121

    How do you factor
    The first and third have a leading coefficient of 1. So you know that the first terms have to be
    x^2 + 9x + 20 = ({\color{red}x}\;+\;?)({\color{red}x}\;+\;?)
    To fill in the last terms, ask yourself, what are the factors of 20 whose sum is 9? It's +4 and +5, so fill them in:
    x^2 + 9x + 20 = (x\;+\;{\color{red}4})(x\;+\;{\color{red}5})

    The second and fourth are one of the special patterns that you should memorize -- these involve difference of two squares. The pattern is
    a^2 - b^2 = (a + b)(a - b)
    a would correspond to s, and b would correspond to 10:
    s^2 - 100 = s^2 - 10^2 = (s\;+\;10)(s\;-\;10)

    I'll let you try the other two.


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    Last edited by yeongil; June 21st 2009 at 03:05 PM.
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