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# C3 differentiation help

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1. Hi,

There's a few differentiation questions that I'm stuck on.

f (x)= (-4x)/((1+x^2)^2)
I started doing it by using the quotient rule but I can't get to the answer at the back of the book.

f (x) = x ((9-2x^2)^1/2)
The first part of the question was to work out f'(x) of (9-2x^2)^1/2 which I did using chain rule.
The next part of the question's to work out f'(x) of the whole function which I tried to do using the product rule but I keep getting it wrong.

I also had a problem with differentiating (2x-1)^3 (x+1)^3 as I wasn't sure which rule/rules to use in which order.

Any help on any of the questions would be really appreciated
2. (Original post by VioletPhillippo)
Hi,

There's a few differentiation questions that I'm stuck on.

f (x)= (-4x)/((1+x^2)^2)
I started doing it by using the quotient rule but I can't get to the answer at the back of the book.

f (x) = x ((9-2x^2)^1/2)
The first part of the question was to work out f'(x) of (9-2x^2)^1/2 which I did using chain rule.
The next part of the question's to work out f'(x) of the whole function which I tried to do using the product rule but I keep getting it wrong.

I also had a problem with differentiating (2x-1)^3 (x+1)^3 as I wasn't sure which rule/rules to use in which order.

Any help on any of the questions would be really appreciated
Well firstly, it's hard to help when nobody knows where exactly you went wrong because you seems to have solid methods.

Secondly, I'd ignore the product rule on that last one because

then just chain rule it.
3. (Original post by RDKGames)
Well firstly, it's hard to help when nobody knows where exactly you went wrong because you seems to have solid methods.

Secondly, I'd ignore the product rule on that last one because

then just chain rule it.
Thanks, I've done the last question correctly now . For the 1st question using the quotient rule I got as far as subbing in the values (1+x^2)^2 (-4x) - (-4)(4x+4x^3) /(1+x^2)^4 but I'm struggling with the simplifying without expanding it out.

Question 2, using the product rule I subbed in x (-2x/((9-2x^2)^1/2) + 1 ((9-2x^2)^1/2) but again I'm struggling with the simplifying.

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