Question

Question #a7258

Answer 1

`f'(x)=-3sin(3x)`

Explanation:

Here are some things to remember:
If `f(x)=cos(x)`, then `f'(x)=-sin(x)`
And also the chain rule: If `f(x)=g(h(x))`, then `f'(x)=g'(h(x))*h'(x)`

Let's say that `g(x)=cos(3x)` and `h(x)=3x`
We need to find the derivative of both `g(x)` and `h(x)`
`g'(x)=-sin(3x)` and `h'(x)=3`

We multiply these two to get: `f'(x)=-3sin(3x)` This is the answer!