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Math Help - rational expressions. help plz!

  1. #1
    Junior Member
    Joined
    Feb 2008
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    rational expressions. help plz!

    When mutiplying this...

    x - 5x + 4 X x + 2x - 3
    x + 3x - 28 x + 10x +21

    ...is to factor out?

    But, what do i do if i can't find out factors?? Because im not sure how to factor them
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  2. #2
    Senior Member topher0805's Avatar
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    Left Side:

    \frac {x^2 - 5x + 4}{x^2 + 3x - 28}

    Use the sum and product method.

    The top equates to:

    (x-4)(x-1)

    And the bottom equates to:

    (x+7)(x-4)

    The (x-4) terms cancel out so the left side of your expression is:

    \frac {x-1}{x+7}

    Right Side:

    \frac {x^2 + 2x - 3}{x^2 + 10x +21}

    The top equates to:

    (x+3)(x-1)

    The bottom equates to:

    (x+3)(x+7)

    The (x+3) terms cancel out, so your right side expression is:

    \frac {x-1}{x+7}

    Rules of fractions say that we simply multiply the top by the top, and the bottom by the bottom to get:

    <br />
\frac {(x-1)^2}{(x+7)^2}
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