Simple application of Derivitives problem

  • Thread starter Leonidas
  • Start date
  • #1
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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?
 

Answers and Replies

  • #2
Pyrrhus
Homework Helper
2,178
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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]
 
  • #3
20
0
oh.

...

1. That was really fast... thanks.

2. I should have seen that.

3. :smile:
 

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