You are Here: Home

# Chain Rule? Tweet

Maths and statistics discussion, revision, exam and homework help.

Announcements Posted on
Enter our travel-writing competition for the chance to win a Nikon 1 J3 camera 21-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
1. Chain Rule?
Me again.

Basically, I was taught the chain rule today along with the quotient and product rules and I could do all the question involving them except this one:

Differentiate the following function:

Thanks,
Sora
2. Re: Chain Rule?
Can you differentiate ln

This is just the chain rule but with 3 functions
3. Re: Chain Rule?
I used chain rule twice, but not sure that's the best way to do it...
4. Re: Chain Rule?
3 functions?

So far I have:

Is this right?
5. Re: Chain Rule?
(Original post by Sora)
3 functions?

So far I have:

Is this right?
For du/dx, you forgot to multiply by 2x as (x^2 -1) differentiated is 2x and your dy/du should just be 1/U, not 1/x.
Last edited by samir12; 20-06-2012 at 18:22.
6. Re: Chain Rule?
Is my "U" wrong? I think it's meant to be just (x^2 -1)
7. Re: Chain Rule?
Your U is right, it's your dU/dx that is wrong. Apply the chain rule again to find du/dx.
8. Re: Chain Rule?
(Original post by Sora)
Is my "U" wrong? I think it's meant to be just (x^2 -1)
It doesnt matter as long as you differentiate correctly, this question is more complex as you have 3 functions, within each other, the ln the (..)^1/2 and the x^2-1 so you have to use the chain rule when finding du/dx.
9. Re: Chain Rule?
Isn't it just the differential of the equation in the brackets of ln over the original function of ln?
10. Re: Chain Rule?
Two-step chain rule (two substitutions)...

Let and , then .

So (chain rule):
11. Re: Chain Rule?

12. Re: Chain Rule?
Thanks for all your help. I think I sort of combined the methods shown and figured it out.

I did:

then to find I used the chain rule again to get
and I used and then did:

Sorry if it is hard to follow xD
13. Re: Chain Rule?
(Original post by Sora)
Thanks for all your help. I think I sort of combined the methods shown and figured it out.

I did:

then to find I used the chain rule again to get
and I used and then did:

Sorry if it is hard to follow xD

That is fine
14. Re: Chain Rule?
Thank you