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Math Help - Finding the diagonal

  1. #1
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    Exclamation Finding the diagonal

    The width of a rectangle is 2 less than twice its length. If the area of the rectangle is 54 cm, what is the length of the diagonal?

    Note: Your answer must be a number. It may not contain any arithmetic operations.

    For this i have done:

    A = lw

    so

    54= l ( 2l - 2)
    54= (2l^2 - 2l)
    54 = 2l ( l -1)

    This seems wrong...
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  2. #2
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    Re: Finding the diagonal

    Looks OK to me, solve using the quadratic formula.
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  3. #3
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    Re: Finding the diagonal

    so set it all equal to 0?

    would it be

    0= 2l^2 - 2l - 54?
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  4. #4
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    Re: Finding the diagonal

    OK, I got l = 5.72 and w = 9.44

    and now i just do pythagorean theorem to find the diagonal
    thanks!
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