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# Edexcel A2 C4 Mathematics June 2015 - Official Thread Watch

1. (Original post by Moniii16081997)
I don't think you can do that, that only works when you differentiate.

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It becomes

Which you then make:

2. (Original post by 13 1 20 8 42)
Use the double angle formula for cos2y
can someone help me with june 13 replacement paper. Q4b ? i understand what they done in the mark scheme, but why couldn't i have taken out (10,000)^1/3 as this would lead me to still getting x=0.81 and that is still valid ? as x is less than 8/9? i tried this way and multiplied (10,000)^1/3 at end to the expansion too but dont get the same answer, get something like 24... ? pls can someone help, this is driving me crazy! many thanks. Do you mind helping me out pls
3. How do you do part a

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4. Has anyone June 2006?
Question 3b I know u use volume of revolution formula. I also get u use 1/2(1-cos2A) formla for sin^2(x/2) however I am not sure what happens to the x/2 when they write it out again it just disappears from the working out Not sure why that is ???

https://a086a5a2f39bda93734c56a63fab...%20Edexcel.pdf
5. (Original post by Maths degree)
can someone help me with june 13 replacement paper. Q4b ? i understand what they done in the mark scheme, but why couldn't i have taken out (10,000)^1/3 as this would lead me to still getting x=0.81 and that is still valid ? as x is less than 8/9? i tried this way and multiplied (10,000)^1/3 at end to the expansion too but dont get the same answer, get something like 24... ? pls can someone help, this is driving me crazy! many thanks. Do you mind helping me out pls
x = 0.81? If you take out 1000^(1/3) from 7100^(1/3) you get 7.1^(1/3) and so set 8 - 9x = 7.1, I'm not quite sure what you did.
6. If you want to integrate cos^2 (y) you use the formula cos2y=2cos^2 (y) -1 which then becomes 1/2 + 1/2cos2y =cos^2 (y) and then you integrate that to get 1/2(x) + 1/4sin(2x) +c
7. For vectors when finding an angle do we use the numbers in radians or in degrees?

Does it matter for c4 what mode the calculator is in?
8. can anyone help me with this question pleaaaassee? I don't get how they got it
9. (Original post by ~amethyst~)
For vectors when finding an angle do we use the numbers in radians or in degrees?

Does it matter for c4 what mode the calculator is in?
Yes, all the mark schemes I have looked at have always stated that the angle must be in degrees.
10. I am aware that Ln |x| differentiates to 1/x, however when you have equations involving for example 48/x or 48/x^2 can I simply convert it to 48x^-1 and 48^x-2?

That would integrate to 48Ln |x| but then would the other integrate to -48^-1?
11. Do u guys think this paper will be of the same standard of previous papers, which are relatively easy, or will it be different like the C3 exam

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12. (Original post by raypalmer)
Do u guys think this paper will be of the same standard of previous papers, which are relatively easy, or will it be different like the C3 exam

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Feeling a standard paper tbh

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13. (Original post by Wahid1)
Feeling a standard paper tbh

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Hmm, c3 caught me by surprise, most of the past papers were decent

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14. C4 C4 C4.......
Spoiler:
Show
My expectation; a dirty or a piss easy paper, nothing in-between!
15. (Original post by 13 1 20 8 42)
x = 0.81? If you take out 1000^(1/3) from 7100^(1/3) you get 7.1^(1/3) and so set 8 - 9x = 7.1, I'm not quite sure what you did.
i took out (10,000)^1/3 so i would set 8-9x = 0.71 to get x=0.81 ? why cant you do it this way ?
16. (Original post by Moniii16081997)
How do you do part a

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Starts from the regular formula for a cone (as proved in the video just fyi)

Basically, in this case the radius is 'h' because if you split the triangle up the middle you end up with two triangles, that each have two 45 degree angles. (which are isosceles) and one 90 degree angle. because there are isosceles, if the height in 'h' then the base is also 'h' (not the hypotenuse)

I wish i could attach a photo but my phone is fudged up
17. (Original post by Maths degree)
i took out (10,000)^1/3 so i would set 8-9x = 0.71 to get x=0.81 ? why cant you do it this way ?
I think that it might because these expansions are more accurate with less terms for smaller values of x
When you have something like 0.81 which isn't too far from the upper limit 8/9, by just using the first few terms of the series you don't get a very good estimate; whereas if you use a smaller x, after a few terms the terms quickly become very small so your estimate isn't too far from the actual value.
18. Where can i find hard c4 papers

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19. (Original post by 13 1 20 8 42)
I think that it might because these expansions are more accurate with less terms for smaller values of x
When you have something like 0.81 which isn't too far from the upper limit 8/9, by just using the first few terms of the series you don't get a very good estimate; whereas if you use a smaller x, after a few terms the terms quickly become very small so your estimate isn't too far from the actual value.
oh okay. thank you very much for your help!
20. (Original post by ~amethyst~)
For vectors when finding an angle do we use the numbers in radians or in degrees?

Does it matter for c4 what mode the calculator is in?
Degrees

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