Posted by **engmath** on Tuesday, February 9, 2010 at 9:12pm.

Find f'(c) if f(x)=-3e^(x+2)+ e^(-5)

[NOTE:A small algebraic manipulation is needed first to get f(x) into a form so that the derivative can be taken and your answer isn't a # but rather a formula that returns and answer.]

attempt at the problem:

3e^(x+2)=e^(-5)---->ln both sides

3^(x+2)=-5

f(x)=3^(x+2)+5

so then: f'(x)=3^(x+2)*ln(3)

This answer is incorrect and I don't know what else to do. I also tried to just take the derivative without manipulating the problem and my answer was still incorrect. Please help. Thank you!!

- Calculus -
**bobpursley**, Tuesday, February 9, 2010 at 9:18pm
-3e^(x+2)=e^(-5)

e^{-3(x+2)}=e^{-5}

now take the ln of both sides.

- Calculus -
**engmath**, Tuesday, February 9, 2010 at 10:40pm
after you ln both sides you end up with

-3(x+2)=-5

-3x-6=-5

f(x)= -3x-1

f'(x)= -3

unfortunately that was not correct either, but I appreciate your help! :)

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