Need Help- Math Problem

Discussion in 'General Discussions' started by rarehunternick, Jan 27, 2009.

  1. rarehunternick

    rarehunternick Level II

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    Ok, so here is the problem

    Now, i tried doing the problem myself. It says that one of my answers are wrong. So, here is what i got

    V= x(19-2x)(6-2x)
    a= 3
    b= 19/2 or 9.5

    I don't know which one i got wrong, so can someone point out what i did wrong? I drew the box and labeled the sides that I know, but i might have something off. Please and thank you!
     
  2. lazypando

    lazypando Level IV

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    What do you mean by a open box? Is it just a box without a top and bottom or is it a box without a top?
     
  3. rarehunternick

    rarehunternick Level II

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    without a top. Forgot to mention that
     
  4. lazypando

    lazypando Level IV

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    so then can you cut the material up or does the box have to be made from one contiguous piece of material (if it has to be contiguous, then it's not possible to make from a rectangular peice of material unless you overlap some stuff)?
     
  5. mjnskivt

    mjnskivt Level III

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    The domain should be x=0 to x=9.5
    In your equation, you have x(19-2x)(6-2x)
    That is a third power equation, so there are 3 routes: x=0, x=3, and x=9.5
    So while at x=3 the volume is zero, the domain ranges from 0 to 9.5
     
  6. Hally

    Hally Level IV

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    Mjn you jerk, you beat me to another homework question :(

    Save some joy for a bedridden engineering student who can't go to class.

    EDIT: I found a mistake in what you said. there are three ROOTS. not three ROUTES. :D
     
  7. rarehunternick

    rarehunternick Level II

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    actually, you may still be able to solve it. For some reason, when i submitted my answers, i got the response that 1 of my answers is incorrect. So, their is still a chance. I'm thinking their is something either wrong with the formula or the domain
     
  8. Hally

    Hally Level IV

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    AHA! I see where the mistake is.

    mjn found the domain for the value of X. we're looking for the domain of the volume.

    The minumum volume is zero.

    Maximize the volume by taking the formula and finding the maximum.

    Or find the derivative and find the roots to find local min/maxes.

    V = x(19-2x)(6-2x)
    V = x(114 + 4x^2 - 50x)
    V = 4x^3 - 50x^2 + 114x

    V' = 12x^2 - 100x + 114.


    Find where that last function equals zero, and you have local max/mins. Test each of them, and see which works for the maximum volume. I'm too tired now, and sans calculatrice.
     
  9. mjnskivt

    mjnskivt Level III

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    :D come on!
    Why would they write "the domain of the volume"?
    Just call it the range like everyone else does.
    When I first saw it I thought it was a maximization problem, but then domain confused me.
    You've won the battle, Hally, but not the war >:)
     
  10. Hally

    Hally Level IV

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    the domain of the volume is:

    0 <= X <= 1.36