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Calculus problem please help

  1. May 17, 2009 #1
    Calculus problem...please help!!!

    1. The problem statement, all variables and given/known data

    Here is a picture of the problem: http://i3.photobucket.com/albums/y62/Phio/23.jpg" [Broken]

    2. Relevant equations

    A = xy = 780

    cost = 8x+2y

    3. The attempt at a solution

    c = 8x + (1560/x)

    c'= 8 - ( 1560/(x^2) )

    0 = 8 - ( 1560/(x^2) )



    x^2 = 195

    x= [tex]\sqrt{195}[/tex]

    x = 13.96 = 14


    I don't know what to do from here...I still can't figure out what the answer is. I think it must be either B or D.

    Please help...thank you!!!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 17, 2009 #2

    rock.freak667

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    Homework Helper

    Re: Calculus problem...please help!!!

    Find the corresponding value of y.
     
  4. May 17, 2009 #3
    Re: Calculus problem...please help!!!

    oh now I see it...it's obvious. The answer is B.

    Thanks!
     
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