## sandy524 3 years ago find the derivative of f(x) = 3x cos 6x .

1. Mimi_x3

$\frac{d}{dx}3xcos6x$ Do you know the product rule?

2. sandy524

yes

3. Mimi_x3

So, what have you done?

4. sandy524

but how would i use it in this case

5. Mimi_x3

Where are you having problems?

6. sandy524

may someone please show me step by step how to do this. my professor sucks and is currently being investigated by the math dept here because of it so yeah...

7. tinagca

8. tinagca

That site will provide you with a step by step! :D

9. sandy524

mathway is not credible

10. Mimi_x3

Well, have you atleast tried it?

11. tinagca

How i learn a lot from that site...

12. tinagca

You just have to sign up to get the step by step part!! :) It helps me a ton...

13. sandy524

i have missed many questions from its wrong answers. wolframalpha is more reliable

14. tinagca

Okay. maybe you just type them in wrong... it always helps me :D

15. tinagca

I dont use it for tests though... i use it for help... you use it for tests?

16. sandy524

okay sure but anyways thanks bye. now back to the question i need help with

17. Mimi_x3

@tinagca: Please don't divert people to another site; when someone is trying to help them.

18. tinagca

Mkay! later :D

19. tinagca

I was trying to give her a step by step site :o

20. Mimi_x3

That was retarded; interjecting out of the blue.

21. sandy524

please folks i really need help the bantering can be spared

22. tinagca

Oh shut up. like seriously i was trying to help then you guys started being rude. So whatever, a simple thank you and just saying " Oh i already tried that site" would have been fine.

23. zepdrix

|dw:1350314820570:dw|

24. sandy524

thank you zepdrix u are always so helpful

25. zepdrix

so do it piece by piece :) We have a (3x)', what is the derivative of 3x? :D

26. sandy524

simply 3

27. zepdrix

ok cool, so the first term will simplify to (3)(cos6x). Hmm now we have a (cos6x)' on the right side. We'll take the derivative of the outermost function (cosine) Then "chain" (multiply by the derivative of the inside (6x)' ) So whats the derivative of cos6x? :D

28. sandy524

-6sin(6x)

29. sandy524

right

30. zepdrix

Yay sandy \c:/

31. tinagca

You should give @zepdrix a medal @sandy524 ...i mean, that was a great answer!

32. zepdrix

lol tina c:

33. tinagca

:) I gave you a medal! :D

34. sandy524

ok so after that what do we do

35. zepdrix

Just combine the pieces together and simplify :D So far we've figured out that the derivative is (3)(cos6x) + (3x)(-6sin6x) =3cos6x -18xsin6x Make sense? :D