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# some questions about differentiating (C3) Watch

1. Hey so i'm someone who doesn't get extra time so I like to be as efficient as possible in the exam (although I 100% run out of time in economics no matter what I do but thats a different subject).
My question is: for a question requiring for example the product rule, would I be able to just write down the answer without any working? For example seeing as it's the derivative of the 1st x 2nd plus derivative of 2nd x 1st there is no need for all the u = this and v= this... because it wastes time which I know i'll need in another question?
If not, if i were to write down the equation then say "by product rule" and then give my answer would that get full marks provided the answer is correct?
Same question applies for quotient rule.

Secondly, I was looking at this ^ c3 i.y.g.b paper and whilst attempting question 2 the normal way it just came out very very long but once I looked at the mark scheme the guy/girl took Ln of both sides then differentiated it and it seemed way less time consuming. Is there a way to tell whether taking Ln is faster than quotient/product rule methods or just better in general?
mark scheme ^
2. (Original post by Icyytea)
Hey so i'm someone who doesn't get extra time so I like to be as efficient as possible in the exam (although I 100% run out of time in economics no matter what I do but thats a different subject).
My question is: for a question requiring for example the product rule, would I be able to just write down the answer without any working? For example seeing as it's the derivative of the 1st x 2nd plus derivative of 2nd x 1st there is no need for all the u = this and v= this... because it wastes time which I know i'll need in another question?
If not, if i were to write down the equation then say "by product rule" and then give my answer would that get full marks provided the answer is correct?
Same question applies for quotient rule.

Secondly, I was looking at this ^ c3 i.y.g.b paper and whilst attempting question 2 the normal way it just came out very very long but once I looked at the mark scheme the guy/girl took Ln of both sides then differentiated it and it seemed way less time consuming. Is there a way to tell whether taking Ln is faster than quotient/product rule methods or just better in general?
mark scheme ^
I never bother with any of the u and v stuff except for integration by parts. It's much easier to just remember how it works and get straight to it.
3. (Original post by Icyytea)
Hey so i'm someone who doesn't get extra time so I like to be as efficient as possible in the exam (although I 100% run out of time in economics no matter what I do but thats a different subject).
My question is: for a question requiring for example the product rule, would I be able to just write down the answer without any working? For example seeing as it's the derivative of the 1st x 2nd plus derivative of 2nd x 1st there is no need for all the u = this and v= this... because it wastes time which I know i'll need in another question?
If not, if i were to write down the equation then say "by product rule" and then give my answer would that get full marks provided the answer is correct?
Same question applies for quotient rule.

Secondly, I was looking at this ^ c3 i.y.g.b paper and whilst attempting question 2 the normal way it just came out very very long but once I looked at the mark scheme the guy/girl took Ln of both sides then differentiated it and it seemed way less time consuming. Is there a way to tell whether taking Ln is faster than quotient/product rule methods or just better in general?
mark scheme ^
it all depends on the markscheme as examiners rely and refer to it to give you a grade on each paper so if the ms requires methods to be shown therefore if the methods are not shown then you will probably lose method marks sometimes if a candidate doesn't get the correct final answer but shows correct method he or she receives some marks so it's worthwhile.

as
4. (Original post by jbaten)
it all depends on the markscheme as examiners rely and refer to it to give you a grade on each paper so if the ms requires methods to be shown therefore if the methods are not shown then you will probably lose method marks sometimes if a candidate doesn't get the correct final answer but shows correct method he or she receives some marks so it's worthwhile.

as
(Original post by Icyytea)
Hey so i'm someone who doesn't get extra time so I like to be as efficient as possible in the exam (although I 100% run out of time in economics no matter what I do but thats a different subject).
My question is: for a question requiring for example the product rule, would I be able to just write down the answer without any working? For example seeing as it's the derivative of the 1st x 2nd plus derivative of 2nd x 1st there is no need for all the u = this and v= this... because it wastes time which I know i'll need in another question?
If not, if i were to write down the equation then say "by product rule" and then give my answer would that get full marks provided the answer is correct?
Same question applies for quotient rule.

Secondly, I was looking at this ^ c3 i.y.g.b paper and whilst attempting question 2 the normal way it just came out very very long but once I looked at the mark scheme the guy/girl took Ln of both sides then differentiated it and it seemed way less time consuming. Is there a way to tell whether taking Ln is faster than quotient/product rule methods or just better in general?
mark scheme ^
If your answer is mathematically correct then you will get the marks. For the chain rule, product rule, and quotient rule, there is certainly no need to write down u and v: just write down the expression using the required rule, and then simplify it algebraically.

Logarithmic differentiation will generally be faster when you have a product or quotient involving several functions. If you only have 2 functions multiplied/divided then the product/quotient rule is faster.
5. Sometimes if its one I can do in my head or with minimal working I just write

u = stuff v = stuff
du = stuff dv = stuff

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