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Homework Help: Simple application of Derivitives problem

  1. Nov 7, 2004 #1
    Find two positive numbers that satisfy the given requirements.

    The Product is 192 and the sum is a minimum.

    I said that x*y=192 and y=192/x and that dy/dx= -192/x^2

    I thought that we were supposed to set the derivitive equal to zero in order to find the local extrema... however -192/x^2 does not equal 0...right???

    I'm dazed and confused... can someone please help?
  2. jcsd
  3. Nov 7, 2004 #2


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    Homework Helper

    You should have done

    [tex] xy = 192 [/tex]

    [tex] y = \frac{192}{x} [/tex]

    [tex] x + y = (number) [/tex]

    Minimize this:
    [tex] x + \frac{192}{x} = (number) [/tex]
  4. Nov 7, 2004 #3


    1. That was really fast... thanks.

    2. I should have seen that.

    3. :smile:
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