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Math Help - Another quad formula word prob

  1. #1
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    Another quad formula word prob

    Block 4 by 5 by 3 feet. Wants to reduce volume by shaving off the same amount from length width and height.

    Could you give me a clue as to where I should start? I know I have to make a quad formula.

    The answer is -x^3+12x^2-47x+60
    Last edited by RaphaelB30; August 28th 2009 at 05:33 AM. Reason: add more info
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  2. #2
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    V=h \cdot l \cdot w

    If we're subtracting the same amount from each value:

    V=(h-x)(l-x)(w-x)

    Substitute in for the values of h, w, and l:

    V=(4-x)(5-x)(3-x)

    Multiply it out:

    V= (20-9x+x^2)(3-x)


    V= 60-27x+3x^2-20x+9x^2-x^3 = -x^3+12x^2-47x+60

    Also, it isn't quadratic, but rather, a cubic...but I suppose you make a quadratic in one of the intermediate steps.
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