# If #f(x) =xe^(5x+4) # and #g(x) = cos2x #, what is #f'(g(x)) #?

##### 2 Answers

#### Answer:

#### Explanation:

whilst the intention of this question may have been to encourage the use of the chain rule on both

to make the point we look at the definition

or

the prime means differentiate wrt to whatever is in the brackets

here that means, in Liebnitz notation:

contrast with this the full chain rule description:

So, in this case,

So here

by the product rule

So

in short

#### Answer:

#### Explanation:

To find

Let us substitute