## zurf Find the derivative of f(x) = -cos (2x^2-3) one year ago one year ago

1. wio

Do you know how to use the chain rule?

2. zurf

yeah yes i do

3. wio

Well your inner function is $$2x^2-3$$ and your outer function is $$-\cos(x)$$. There shouldn't be anything hard about this.

4. zurf

do we have to use chain rule ? i'm confused on what we should do when with the -cos

5. wio

The - is just $$-1\cdot \cos(x)$$. It's a constant. You can pull it out and put it back in after.

6. zurf

oh really? but this have to use f(x+h)-f(x) first derivation ..

7. wio

You have to use this you mean? $\Large \lim_{h\rightarrow 0}\frac{f(x+h)-f(x)}{h}$

8. wio

You're not allowed to use the chain rule?

9. zurf

Oh sorry, i just realised it only has to use chain rule. I make things go more complicated -_-

10. wio

So can you do it now?

11. zurf

yeah the answer is sin(2x^2-3)(4x) right ?

yeah, i agree that

13. zurf

Oh thank you so much :D

14. wio

It's correct.