This is the equation I have:

Let $\displaystyle f(x) = -4 \ln(5 x) $

Find $\displaystyle f'(x) = $

My Work Sheet says the answer is:

$\displaystyle

-4/x

$

My question is, shouldn't it be somthing like:

$\displaystyle

-20/5x

$

...when you derive $\displaystyle ln(5 x)$ shouldn't it become $\displaystyle 1/5x$ and from there don't you have to use the chain rule on $\displaystyle 5x$ and get 5?

It seems to me you would only get $\displaystyle -4/x $ if $\displaystyle f(x) = -4 \ln(x)$

What is it I don't understand?! Thank You