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# The Edexcel C4 (21/06/12 - PM) Revision Thread Tweet

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1. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by DoctorVertigo)
Need a D in this paper for an A! Sorted!
Same. I got a B in C3 so no A*
Don't wanna repeat it

C4 grade boundaries r pretty high.
2. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by This Honest)
Same. I got a B in C3 so no A*
Don't wanna repeat it

C4 grade boundaries r pretty high.
I woulda thought c4 grade boundaries would be lower?
3. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by Azii)
I woulda thought c4 grade boundaries would be lower?
Jan 12 or june 11 was 46 for a D I think which IMO is high
4. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by Azii)
Can anyone help me on this? I hate these types of questions..

The area A of a circle is increasing at a constant rate of 1.5 cm^2s^–1. Find, to 3 significant figures, the rate at which the radius r of the circle is increasing when the area of the circle is 2 cm^2.
Is this from the textbook?

When A=2

From (1)

You need to find the rate at which the radius is increasing, which is

5. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
Gawd. I want/kinda need to get an A* in this. Starting the revision tomorrow.
Anyone else use them CGP Edexcel A2 Maths revision books? I think they are amazing, well written, and explains every concept effectively, has warm up q's, end of topic Exam q's and 2 Practice papers.
6. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
integration by subsituiton: = u^2=2+x ⇒ 2udu=dx

can someone explain to me how to get there from here u^2=2+x ?
i thought im going tend up with 2du=dx...i dont know where the u comes from?
any help would be appreciated
7. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
any help on this question?

The points A and B have position vectors 5i + 11k and ci + dj + 21k respectively, where c and d
are constants.
The line l, through the points A and B, has vector equation r = 5j + 11k + λ(2i + j + 5k), where λ
is a parameter.
(a) Find the value of c and the value of d. (3)

The point P lies on the line l, and OP is perpendicular to l, where O is the origin.
(b) Find the position vector of P. (6)
(c) Find the area of triangle OAB, giving your answer to 3 significant figures.

I did part A but cant do part b :'(
Any idea on how to do it?
8. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by arnab)
any help on this question?

The points A and B have position vectors 5i + 11k and ci + dj + 21k respectively, where c and d
are constants.
The line l, through the points A and B, has vector equation r = 5j + 11k + λ(2i + j + 5k), where λ
is a parameter.
(a) Find the value of c and the value of d. (3)

The point P lies on the line l, and OP is perpendicular to l, where O is the origin.
(b) Find the position vector of P. (6)
(c) Find the area of triangle OAB, giving your answer to 3 significant figures.

I did part A but cant do part b :'(
Any idea on how to do it?

using the vector equation gives the the position vector (i.e from origin) of that point.
so OP = (2λ)i + (5+λ)j + (11+5λ) ------ I just added the equation for r.

since OP is perpendicular to l and AB is a part of the line l, dot product of OP and direction vector of l = 0

OP.(2i +j + 5k)=0

this will give you

4λ + 5 +λ + 55 + 25λ = 0

30λ =-60

λ = -2

therefore OP = -4i +3j +k (substituting λ=-2 in OP)

btw this was from the review exercise if I am not mistaken ? Do you need the solution bank for the text book? It will come in handy in later questions ..
9. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by master_blaster66)
integration by subsituiton: = u^2=2+x ⇒ 2udu=dx

can someone explain to me how to get there from here u^2=2+x ?
i thought im going tend up with 2du=dx...i dont know where the u comes from?
any help would be appreciated

when you are differentiating u^2=2+x , you are doing it implicitly.

=> differentiation of (u^2) = differentiation of (2+x)

the differentiation of u^2 = 2u.. but since u is a function (i.e u = sqroot(2+x), u need to differentiate u as well. You write this as du/dx

so left handside = 2u x (du/dx)

therefore 2u x (du/dx) = 1 (right handside)

=> 2udu = dx (multiplying both sides by dx)

10. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
Ugh, starting revision for C3 and C4 tomorrow..

How much time should I spend on C4 in the next 10 days before C3???
11. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by ezioaudi77)
The best place you can find all the log rules we need to know is Edexcel's C2 textbook (follow this link to view it online). It contains only the rules we need to know and also they are well explained. Below is the summary provided and I added the natural logarithm rules

Summary of Exponential and Logarithms

**Remember that .

A function or , where is a constant, is called an exponential.

means that , where is called the base of the logarithm. So means that .

. So, .
. So, .

is sometimes written as .

The laws of logarithms are
. So (the multiplication rule)

. So (the division law)

. So (the power law)

From the power law,
. So

You can solve an equation such as by first taking the logarithms (to the base 10) of each side OR the natural logarithm of both sides. will be

The change in base rule for logarithms can be written as , so .

From the change of base rule, . So

Hope that helps
Thank you
12. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by Callidus)
Ugh, starting revision for C3 and C4 tomorrow..

How much time should I spend on C4 in the next 10 days before C3???
Until you understand all the concepts and can do at least the 2 2011 papers and jan 2012 successfully
13. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
Anyone think that the papers 2005-2009 are quite a bit harder than 2010-12?
14. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by Extricated)
Anyone think that the papers 2005-2009 are quite a bit harder than 2010-12?
Yessssssss
15. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
Hoping to smash this and C3 to get my A*. But I would still be happy with an A xD
16. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
Is there a booklet which has C4 questions from old papers all together?
17. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
(Original post by Extricated)
Anyone think that the papers 2005-2009 are quite a bit harder than 2010-12?

(Original post by This Honest)
Yessssssss
Yep it is definitely noticeable in the grade boundaries as well. Used to be <73 for 100 UMS and has been under 70 a few times but since 2010 it has been 75 almost every time. I'm kinda hoping that this paper is similar to the 05-09 ones.
18. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
how does cosec^2xtan^2x = sec^2x :s
19. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
really need help :/
20. Re: The Edexcel C4 (21/06/12 - PM) Revision Thread
How do you integrate (1+2x)^-2

I did it and got -(1+2x)^-1
you wouldn't multiply the -1 by 2 coz that's the chain rule
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