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Math Help - Word problem;quadratic equation

  1. #1
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    Exclamation Word problem;quadratic equation

    a rectangle has an area of 288 cm(square). if the width is decreased by 1 cm and the length increased by 1 cm, the area would decrease by 3 cm(square). Find the original dimensions of the rectangle.
    Last edited by Ilsa; September 28th 2009 at 12:42 AM.
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  2. #2
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    Quote Originally Posted by Ilsa View Post
    a rectangle has an area of 288 cm(square). if the width is decreased by 1 cm and the length increased by 1 cm, the area would decrease by 3 cm(square). Find the original dimensions of the rectangle.
    I'm not really an expert in this, but here's how I do it.


    L X W = 288

    (L+1) (W-1) = 285
    LW - 1L + 1W - 1= 285
    LW - 1L + 1W = 286

    then i do this:

    .....LW - 1L + 1W = 286
    (-) LW = 288
    ----------------------------
    ..... -L + W = -2
    ..... W = -2 + L

    then i substitute to L x W = 288

    L x W = 288
    L (-2+L) = 288
    -2L + L2 = 288
    L2 -2L - 288 = 0
    (L-18)(L+16) = 0
    L = 18
    L = -16 (this one is rejected because a rectangle cannot have negative sides)

    then substitute to get the value of W
    L x W = 288
    18 x W = 288
    18W = 288
    W = 16

    Answer would be {L=18,W=16}

    That's how i do it. Sorry if I don't know how to put into math code.
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  3. #3
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    Quote Originally Posted by reiward View Post
    I'm not really an expert in this, but here's how I do it.



    Answers would be {L=18,W=16}

    That's how i do it. I don't know about the negative answers though if it's acceptable.
    Just ignore the negative values. You can't have a negative length or width.
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  4. #4
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    Thankyou! your replies have been really helpful!
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