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# Edexcel A2 C4 Mathematics June 2015 - Official Thread Watch

1. (Original post by iceangel8)
Could someone please explain to me part b of this expansion question from June 2013 R it's a simple element but I really don't understand it! Thanks
Well, you've expanded 8-9x cube rooted, and you're asked to find the cube root of 7100. So you ask yourself how you can make 8-9x look anything like 7100. Well, x=1/10 makes it 7.1, so using the expansion you get the cube root of 7.1. But we want the cube root of something a thousand times bigger.

Just like (2*4)^2 = 8^2 = 64 = 4*16 = 2^2 * 4^2, the cube root of 7100 can be split into the cube root of 7.1 and the cube root of 1000 multiplied together. So you get the expansion for 7.1 and multiply by the cube root of 1000, which is 10.
2. (Original post by SeanFM)
Well, you've expanded 8-9x cube rooted, and you're asked to find the cube root of 7100. So you ask yourself how you can make 8-9x look anything like 7100. Well, x=1/10 makes it 7.1, so using the expansion you get the cube root of 7.1. But we want the cube root of something a thousand times bigger.

Just like (2*4)^2 = 8^2 = 64 = 4*16 = 2^2 * 4^2, the cube root of 7100 can be split into the cube root of 7.1 and the cube root of 1000 multiplied together. So you get the expansion for 7.1 and multiply by the cube root of 1000, which is 10.
Honestly thank you so much that is very helpful that's exactly what I needed! Good luck on Tuesday

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3. (Original post by iceangel8)
Honestly thank you so much that is very helpful that's exactly what I needed! Good luck on Tuesday

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You're welcome. if a question like that comes up again, the main thing will probably spotting the right x value but it shouldn't take too much work. Luckily I sat C4 last year, but good luck to you too
4. When writing the integral with ln is it essential to use the modulus sign around the x within the ln?
5. (Original post by joanneeve)
When writing the integral with ln is it essential to use the modulus sign around the x within the ln?
I'd also like to ask this, I have no idea when to use modulus and when to use normal brackets with ln.
6. (Original post by NikolaT)
I'd also like to ask this, I have no idea when to use modulus and when to use normal brackets with ln.
You always have to use the modulus signs and then you can remove them if the question indicates they are not required.
7. Can someone please explain to me what part b) is actually asking for?

8. Does anyone have the link to the C4 IYGB papers/
9. (Original post by joanneeve)
When writing the integral with ln is it essential to use the modulus sign around the x within the ln?
I don't think it's essential to put in working for every question. But, there are certain questions where you may get a negative value inside the ln(x), so then you'd need to use the modulus signs to indicate your working. Otherwise, I think it's fine. I've never been marked down for excluding them.
10. (Original post by RobHunter97)
Can someone please explain to me what part b) is actually asking for?

You just multiply f(theta) by theta

f(theta) is shown in part a, so theta x f(theta) would be (1/2)theta + (7/2)thetacos2theta
11. (Original post by dominicwild)
I don't think it's essential to put in working for every question. But, there are certain questions where you may get a negative value inside the ln(x), so then you'd need to use the modulus signs to indicate your working. Otherwise, I think it's fine. I've never been marked down for excluding them.
okay thankyou! i just automatically do normal brackets so i just want to check i wouldnt loose marks
12. (Original post by nayilgervinho)
Does anyone have the link to the C4 IYGB papers/
http://www.thestudentroom.co.uk/show....php?t=3361905
13. (Original post by joanneeve)
When writing the integral with ln is it essential to use the modulus sign around the x within the ln?
only if there is a chance x may be negative.
14. Hi quick Q
The dy/dx of -2xy
I understand the product rule is applied. But I don't take minus out or do I ?
Ie -(2x dy/dx +2y) which would mean both become negative
OR
-2x dy/dx + 4y which leaves just x negative

Thanks
15. (Original post by kaya_lioness)
Hi quick Q
The dy/dx of -2xy
I understand the product rule is applied. But I don't take minus out or do I ?
Ie -(2x dy/dx +2y) which would mean both become negative
OR
-2x dy/dx + 4y which leaves just x negative

Thanks
take the minus out i would say then use the bracket so theres no confusion of signs
16. (Original post by TeeEm)
no worries

Thank you!!

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17. (Original post by Medicjug)
TeeEm can you link me to some of your questions involving volumes of revolution questions where you have a line and a curve and you use the formula of a cone. I don't know if I am making any sense thanks

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there are some at this link .
..
sorry I cannot give you question number because I am teaching at the moment
18. What's the hardest c4 paper to date?
19. (Original post by anonwinner)
You just multiply f(theta) by theta

f(theta) is shown in part a, so theta x f(theta) would be (1/2)theta + (7/2)thetacos2theta
Thanks, I gave it a go but couldn't get it. Does anyone have a worked example, the mark scheme isn't making much sense to me

The rest of that paper (June 2010) was lovely though, some quite fun questions in there. That question would have been all I dropped marks on
20. (Original post by RobHunter97)
Thanks, I gave it a go but couldn't get it. Does anyone have a worked example, the mark scheme isn't making much sense to me

The rest of that paper (June 2010) was lovely though, some quite fun questions in there. That question would have been all I dropped marks on

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