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Math Help - How to find the length of the sides?

  1. #1
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    How to find the length of the sides?

    A plot of land is a square and its sides are x metres. It gets expanded so that the plot of 40 metres longer and 50 metres wider and so that it is 200 metres short of being double the area of its original size. What is x?

    I have got as far as working out:

    Original Perimeter is 4x
    Original Area is 2x
    New perimeter is 4x + 180
    New Area = 4r - 200 = 2r - 100

    I am unsure where to take it from here though. Help would be appreciated.
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  2. #2
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    Quote Originally Posted by JQ2009 View Post
    A plot of land is a square and its sides are x metres. It gets expanded so that the plot of 40 metres longer and 50 metres wider and so that it is 200 metres short of being double the area of its original size. What is x?

    I have got as far as working out:

    Original Perimeter is 4x
    Original Area is 2x
    New perimeter is 4x + 180
    New Area = 4r - 200 = 2r - 100

    I am unsure where to take it from here though. Help would be appreciated.
    wrong. original area = (x)(x) = x^2
    new area = (x + 50)(x + 40) = x^2 + 90x + 2000

    "so that IT is 200 metres short of being double the area of its original size."
    what is IT?
    is it new area = original area x 2 - 200 square metres????
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  3. #3
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    It is the new area. Which is 200 metres away from being double the original area.
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  4. #4
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    Quote Originally Posted by JQ2009 View Post
    It is the new area. Which is 200 metres away from being double the original area.
    new area = original area x 2 - 200 square metres <---- so is this correct?
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  5. #5
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    Quote Originally Posted by ukorov View Post
    new area = original area x 2 - 200 square metres <---- so is this correct?
    yes.
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  6. #6
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    Quote Originally Posted by JQ2009 View Post
    yes.
    (x+50)(x+40) = 2x^2-200

    x^2+90x+2000 = 2x^2 - 200

    x^2 - 90x - 2200 = 0

    (x-110)(x+20) = 0

    edit: I'm an idiot xD. Didn't see double area
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  7. #7
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    x^2 + 90x + 2000 = 2(x^2) - 200
    -x^2 + 90x + 2200 = 0
    x^2 - 90x - 2200 = 0

    Hence,
    x = [-(-90) +/- (8100 + 4 x 2200)^0.5] / 2
    = (90 +/- 130) / 2
    = 110 or -20

    There cannot be negative value for dimension, so x = 110 metres
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