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# Edexcel C3,C4 June 2013 Thread watch

1. (Original post by lollage123)
to confirm, the integral is

(1/-2ln2) * 2^(2-2x)
How did you get that?
2. (Original post by PoorLoser)
how do you assume what u is in the substitution? when they don;t give it to you? that's the bit i find hard
That's true, it is hard finding a suitable substitution. But sometimes, I find, that even with those that can be easily identified by inspection, the inspection just gets a bit muddly.
3. Quick question, do you ALWAYS have to simplify the direction vector in a vector equation to its simplest form???? pretty sure you have to, or answers will be affected???
4. (Original post by MedMed12)
google exam solutions, edexcel, c4- its the best it goes through exam questions too
good luck!!
Why you avoiding me for
5. (Original post by Riley F.)
Guys, quick help, under what circumstances do you need to do the dot product of a vector line and its own direction vector?
6. (Original post by Kreayshawn)
oh right obviously.
thanks!

does anyone know any other proofs we need to know?
also which shapes area/volume should i memorise?
Volume of cylinder = pi*r^2*h

volume of Sphere = 4/3 * pi * r^3

volume of cone = 1/3 * pi * r^2 * h (h is vertical height)

Surface areas listed under C1 formulae
7. (Original post by MedMed12)
don't they give it in c4 i.e u=x^2+1 ?
Only on the questions that ask you to use substitution but I'm saying that I'll use the technique when trying to integrate the ones that can be done by recognition so I need to work out a suitable substitution first
8. Hi, seems like a stupid question but when I look at the formula booklet of integrating cot it gives a really complicated form, so how would you do this question?
Attached Images

9. what is the differential and integral of (log )base a) X)
10. (Original post by MathsNerd1)
This is what I tend to do as well, although sometimes finding a suitable substitution can take some time
Yes, I agree, it can do. But even with the more simpler integrals, I think I prefer sub as the recognition can sometimes get all muddled I feel aha.
11. differentiate 2^(x^2+4x)

also when you diffrentiate 2^x you get 2^xln2 right
12. (Original post by Knoyle quiah)
Quick question, do you ALWAYS have to simplify the direction vector in a vector equation to its simplest form???? pretty sure you have to, or answers will be affected???
No, you don't have to, but I personally prefer to do it like that.
13. (Original post by Knoyle quiah)
Quick question, do you ALWAYS have to simplify the direction vector in a vector equation to its simplest form???? pretty sure you have to, or answers will be affected???
You don't have to, if you dont simplify you'll just have a multiple of it
14. (Original post by LegendX)
Hi, seems like a stupid question but when I look at the formula booklet of integrating cot it gives a really complicated form, so how would you do this question?
use a trig identity
15. Do we need to be able to find the cartesian equation from a vector equation?
16. (Original post by LegendX)
Hi, seems like a stupid question but when I look at the formula booklet of integrating cot it gives a really complicated form, so how would you do this question?
Just change to cot^2(2x) = cosec^2(2x) - 1
17. (Original post by Chris-69)
Do we need to be able to find the cartesian equation from a vector equation?
No, not for C4.
18. (Original post by justinawe)
No, not for C4.
Thanks
19. (Original post by überambitious_ox)
Yes, I agree, it can do. But even with the more simpler integrals, I think I prefer sub as the recognition can sometimes get all muddled I feel aha.
I don't mind the simpler ones but the more complex ones I tend to go down the substitution route, plus its always good practice to work out substitution by yourself
20. ohmygod I am not ready to be murdered by another replacement paper

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