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# fp2 june 2014 q5 watch

1. http://www.thestudentroom.co.uk/show....php?t=2705197

For the S14 IAL F2 Model answers found in the above thread,

for question 5 part a,

can someone tell me how arsey goes from 2xy''' to 2x(2xy" )
2. (Original post by Katiee224)
http://www.thestudentroom.co.uk/show....php?t=2705197

For the S14 IAL F2 Model answers found in the above thread,

for question 5 part a,

can someone tell me how arsey goes from 2xy''' to 2x(2xy" )
He's differentiating using the product rule.
3. (Original post by Zacken)
He's differentiating using the product rule.
but when you differentiate you get ?
4. (Original post by Katiee224)
but when you differentiate you get ?
Aye, sorry - we have ( means the third derivative of ) differentiating this using the product rule we get:

But we know something about , i.e: that it is the same thing as so we can just replace it into our , so that:

5. (Original post by Zacken)
Aye, sorry - we have ( means the third derivative of ) differentiating this using the product rule we get:

But we know something about , i.e: that it is the same thing as so we can just replace it into our , so that:

At the risk of sounding stupid here... why does ?
6. (Original post by Katiee224)
At the risk of sounding stupid here... why does ?
The question gives us differentiating this:

by using the product rule on the middle term and re-arranging.
7. (Original post by Zacken)
The question gives us differentiating this:

by using the product rule on the middle term and re-arranging.
ohhh they simply got that from the first part of the working and substituted it in to the second

haha i feel super dumb for not spotting that, appreciate the help
8. (Original post by Katiee224)
ohhh they simply got that from the first part of the working and substituted it in to the second

haha i feel super dumb for not spotting that, appreciate the help
No problem.

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