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Is this derivative correct?

  • Thread starter linuxux
  • Start date
  • #1
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Homework Statement



Find derivative of function: [tex]f\left(x\right)=\frac{1}{1+e^{x}}[/tex]

Homework Equations



quotient rule.

The Attempt at a Solution



hopefully this is the solution:
[tex]f^{'}\left(x\right)=\frac{e^{x}}{(1+e^{x})^{2}}[/tex]
 
Last edited:

Answers and Replies

  • #2
1,074
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Really close, but not exactly. Are you sure about the denominator? How is it different from that of the original function?
 
  • #3
133
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oh, thanks! i had that messed up on my paper too.
 
  • #4
dextercioby
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The derivative is okay up to the overall "-" sign which should be absent in the numerator.
 
  • #5
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i think its fixed now...
 
  • #6
dextercioby
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Still incorrect. Remember that

[tex] \frac{d}{dx}\left(\frac{1}{f(x)}\right)=-\frac{f'(x)}{f^{2}(x)} [/tex]
 
  • #7
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oh, i know this should be easy but i've been studying calculus for only 48 hours, so i appreciate the patience and help.

I could easily rewrite the equation like this [tex](1+e^{x})^{-1}[/tex] and derivate it, but i should know how to do it the other way.
 
Last edited:

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