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Math Help - Quadratic Modelling Help

  1. #1
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    Quadratic Modelling Help

    I need a little help with b) ii.
    http://img10.imageshack.us/img10/1038/73...


    Answers to previous questions

    a) i A=y(8+x)-x^2
    ii P=2x+2y+16
    b) i A=192+16x-2x^2

    Thanks
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  2. #2
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    Quote Originally Posted by user_5 View Post
    I need a little help with b) ii.
    http://img10.imageshack.us/img10/1038/73...


    Answers to previous questions

    a) i A=y(8+x)-x^2
    ii P=2x+2y+16
    b) i A=192+16x-2x^2

    Thanks
    Simply solve equation b) for x, and those are the allowable x values. Quadratic formula.
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  3. #3
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    Solving for x using the quadratic formula gives.

    x=4 \pm 4\sqrt7

    Whereas the answer is
    0<x<12
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  4. #4
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    Quote Originally Posted by user_5 View Post
    Solving for x using the quadratic formula gives.

    x=4 \pm 4\sqrt7

    Whereas the answer is 0<x<12
    Since P = 64 you have y = 24 - x. Also, from the diagram it's clear that you require y \geq x.

    These two things can only happen if 0 \leq x \leq 12.

    And since A > 0 is satisfied for these values of x, 0 \leq x \leq 12 is the answer.
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