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# Edexcel A2 C4 Mathematics June 2015 - Official Thread watch

1. cmon! I need a high A in this
2. (Original post by Humbers)
r = radius so it will be the width of the base i guess

if you're asking because of that volume of revolution question in the recent paper (can't remember which) r = the y value

Just think about how it will look when rotated and its the radius of the cone formed
3. (Original post by studentwiz)
No worries, best of luck in the exam
4. i can't really tell when do we use substitution and when do we use integration by parts if not told i the question.. please help!
5. A bit last minute here but how do you know what to substitute in for x in a binomial expansion when it tells you to expand it and then find an approximation for (2)^0.5?

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6. (Original post by studentwiz)
I don't see how people are doing past paper questions, maths has to be the worst exam you can cram for.
Relax and accept that you won't be able to apply a method you learnt an hour before the exam to a completely different question.
7. (Original post by joe1545)
I don't see how people are doing past paper questions, maths has to be the worst exam you can cram for.
Relax and accept that you won't be able to apply a method you learnt an hour before the exam to a completely different question.
are you talking from experience?
8. (Original post by saycheese:))
i can't really tell when do we use substitution and when do we use integration by parts if not told i the question.. please help!
Often for a substitution question you'll be told which substitution to use. For parts you will be integrating functions like Ln(x), xLn(x), xsin(x), x^2sin(x) etc.If an integral requires inspection then the q will only be worth 2 marks. Parts is usually 4 marks. A good tip is to look how many marks the question is worth.
9. (Original post by frozo123)
are you talking from experience?
Yes I am, last years exam ****ed me over and I ended up 10 Ums off an A*..
10. (Original post by problemq)
Often for a substitution question you'll be told which substitution to use. For parts you will be integrating functions like Ln(x), xLn(x), xsin(x), x^2sin(x) etc.If an integral requires inspection then the q will only be worth 2 marks. Parts is usually 4 marks. A good tip is to look how many marks the question is worth.
thanks! do have tips on inspection? i find them hard
11. (Original post by JShell)
r is the radius of the circle and h is the slanted height of the cone.
H is not the slanted height it is the height perpendicular to the radius

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12. (Original post by saycheese:))
thanks! do have tips on inspection? i find them hard
Examples of inspection integrals:
Integrate xsqrt(x^2 + 1), (1+x)^(1/3), xcos(x^2), etc. You need to use reverse chain rule so take an appropriate guess and put a constant in front (think through reverse chain rule) so that your answer differentiates to the integrand. (You should check it works)

I can't give too much detail now but if you totally don't understand inspection, you can use substitution on all of these actually, the substitutions are u=x^2 +1, u=1+x, u=x^2 respectively to the above problems.
13. Anyone else really scared for this exam?! Good luck!
14. Integration by inspection is a 'quick' way of doing integration by substitution, the latter of which is more systematic I'd say.
15. (Original post by Sataris)
Can anyone give me an example of a trig integration by parts where I have to sub it back in at the end? Don't think I've come across one.
IYGB, C4, Paper N I think

http://www.thestudentroom.co.uk/show....php?t=3361905

or

Q26 in
16. (Original post by asjdj)
When you realize you're on your period few hours before the exam.. nooooooooooooooooooooooooooooooo ooooooooooooo
That was me yday :'( stay strong 💪🏻

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17. I'm aiming for a high U in this exam - I think that is achievable?
18. C4 has just started for some...
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19. Good luck fellas

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