1. ## derivatives

my question is write down the derivatives of the following

F(x) =x^7 and g(x) = cos(4x)

For these I got

f'(x)=7x^6 and g'(x) -4 cos(4x)

Is this correct.

The second part says differentiate the function using the product rule.

This bit I am confused

2. $g(x) = \cos 4x$

$g'(x)$ is not $-4\cos4x$

3. can you show me where i have gone wrong

4. Originally Posted by tracy207
can you show me where i have gone wrong
g(x) = cos(4x)
Use the chain rule to find the derivative of g(x)
g'(x) = 4 ( -sin (4x) )= -4sin(4x)
You have to take the derivative of 4x and then take the derivative of the function cosine. I don't see why you need to use product rule here. May be you didn't write the entire question here.