Find the derivative.

Question

y=e^8x/[e^(8x)+9]

y' =

The answer I have is 8e^8x/[(e^8x+9)^2] but it marked it incorrect..

Answer 1

okay here
set u=e^(8x)
v=(e^(8x)+9)

du/dx=8e^(8x)

dv/dx=8e^8x

dy/dx=[(e^8x+9)8e^8x-e^8x(8e^8x)]/(e^8x+9)^2

dy/dx=(8e^64x+72e^8x-8e^64x]/(e^8x+9)^2
=72e^8x/(e^8x+9)^2

check if i mad any erroe

Answer 2

I guess you did.

y' =
(8e^(8x))(e^(8x)+9)-(e^(8x))(8e^(8x))
-------------------------------
        (e^(8x)+9)^2

= 72e^(8x)/(e^(8x)+9)^2

You can use wolframalpha.com to confirm your results:

http://www.wolframalpha.com/input/?i=derivative+e%5E(8x)%2F%5Be%5E(8x)%2B9%5D