# Is this derivative correct?

## Homework Statement

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

quotient rule.

## The Attempt at a Solution

hopefully this is the solution:
$$f^{'}\left(x\right)=\frac{e^{x}}{(1+e^{x})^{2}}$$

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## Answers and Replies

Really close, but not exactly. Are you sure about the denominator? How is it different from that of the original function?

oh, thanks! i had that messed up on my paper too.

dextercioby
Science Advisor
Homework Helper
The derivative is okay up to the overall "-" sign which should be absent in the numerator.

i think its fixed now...

dextercioby
Science Advisor
Homework Helper
Still incorrect. Remember that

$$\frac{d}{dx}\left(\frac{1}{f(x)}\right)=-\frac{f'(x)}{f^{2}(x)}$$

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 $$(1+e^{x})^{-1}$$ and derivate it, but i should know how to do it the other way.

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