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AQA Core 4 Exam Discussion 14/06/2012 !Poll, paper and unofficial MS (first post)!

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Question 1.
ai)

Unparseable latex formula:

\dfrac{5x-6}{x(x-3)} = \dfrac{A}{x} + \dfrac{B}{x-3}[br]\[br]5x-6 = A(x-3) + Bx[br]\[br]Let x = 3 \Rightarrow 9 = 3B \Rightarrow B = 3[br]\[br]Let x = 0 \Rightarrow -6 = -3A \Rightarrow A = 2[br]\[br]\dfrac{5x-6}{x(x-3)} = \dfrac{2}{x} + \dfrac{3}{x-3}[br]

aii)

2lnx + 3ln(x-3) + c

bi)

Unparseable latex formula:

4x^3 +5x -2 = (2x+1)(2x^2 +px + q) + r[br]\[br]Using\ factor\ theorem,\ do\ f(\dfrac{-1}{2})[br]\[br]4(\dfrac{-1}{2})^3 + 5\dfrac{-1}{2} -2 = -5,\ therefore\ r = -5[br]\ [br]Now,\ 4x^3 +5x +3 = (2x+1)(2x^2 +px + q),\ so\ by\ inspection\ p = -1 and q = 3

bii)

Unparseable latex formula:

Now\ divide\ the\ function\ previously\ found[br]\[br]\Rightarrow \dfrac{2}{3}x^3 -\dfrac{1}{2}x^2 + 3x -\dfrac{5}{2} ln(2x+1) + c

Oh! That's clever using the factor theorem. I didn't think of that.
I just did the solving by co-efficients.. (same ans. though) hope they have an alternative answer in the mark scheme!

Reply 821

Iepnauy

I expanded the binomial expansion to x^4.
But I have all the terms up to x^2 correct?

Will I have a mark deducted for it? :colondollar:

Reply 822

Cath-ay

Original post by Sophie1805

Your poll is very subjective, maybe we could have the options for the amount of UMS we reckon we're going to lose as opposed to past papers :]

I've gone down like 20 UMS from past papers.

unfortunately I can't change the poll now. But you can post a new thread with a ums poll if you wish :smile:

Reply 823

SomeoneIveNeverMet

Original post by LGrosvenor101

Thanks

From what I've heard from others, that was definitely not a normal paper, so I am hoping for an A :biggrin:

I need an A, and I'm glad core 4 went OK-ish today otherwise I would pretty much be saying bye bye to my firm :frown:

thanks a lot though! :biggrin:

Me too. I need at least 95%UMS in this paper..know I've definitely dropped 1/2 makrs, maybe 1 more for the |x|<4, if that wasn't the answer. Gaaahh.

I just looked at your name and I know you! I've spoken to you before... I just don't remember what about xD haha (...is Warwick your firm? Or am I thinking of the wrong person..?)

Reply 824

JulietheCat

Original post by Iepnauy

I expanded the binomial expansion to x^4.
But I have all the terms up to x^2 correct?

Will I have a mark deducted for it? :colondollar:

It was only up to x^2 so you could safely discard x^3 and x^4 terms. :smile:

Reply 825

Oromis263

Question 2.

a)

Unparseable latex formula:

sinx - 3cosx[br]\[br]Rsin(x -\alpha) = R(sinxcos\alpha - 3cosxsin\alpha[br]Rcos\alpha = 1[br]Rsin\alpha = 3[br]R = sqrt(10)[br]\alpha = 71.6

Angle x = 32, 291

Writing the working out was tedious for this one, I used general solutions for sin then found x. :smile:

Reply 826

f1mad

Original post by Quexx

Just realised my mistake finding T.. :-(
To do it using logs you need to put 1500(1.015)^n = 1000(1.03)^n
(1.015)^n/(1.03)^n = 2/3
(1.015/1.03)^n = 2/3
n = log{1.015/1.03}(2/3)
Where 1.015/1.03 is the base
n =27.6
T = 28

This was posted from The Student Room's iPhone/iPad App

Yeah I got that. :tongue:

Reply 827

Oromis263

Question 2.

a)

Unparseable latex formula:

sinx - 3cosx[br]\[br]Rsin(x -\alpha) = R(sinxcos\alpha - 3cosxsin\alpha[br]Rcos\alpha = 1[br]Rsin\alpha = 3[br]R = sqrt(10)[br]\alpha = 71.6

Angle\ x = 32, 291

Writing the working out was tedious for this one, I used general solutions for sin then found x. :smile:

Reply 828

Rotravis

Original post by Cath-ay

Hey all,

I've attached today's C4 paper.

Maybe someone can make a detailed unofficial MS?

edit: reuploaded Q6

What were the marks for the question 5? I can't see them on your scan.

Reply 829

stevop21

Had a nightmare on this... just panicked when I knew how to do something but couldn't do it. Have been getting about 60 on past papers. Will be lucky to get 45 on this. Absoloutly gutted doesn't even begin to cover it :frown:

Reply 830

LGrosvenor101

Original post by SomeoneIveNeverMet

I know I got the lxl < 4 wrong, for some reason I remember writing one :L I never really got them to be honest :') it was just that stupid 8 marker at the end, and I made a stupid silly error on the last part of the 1st question :L got the other 8 marker and vectors right though!

And oh... I think I remember speaking to you before, again, cannot remember what about! and yes! Warwick for Chemistry xD Sorry, I cannot remember where you said you were going :frown:

Reply 831

Raj K

Yayy no more maths!!!!!!!!!!!!!!! :biggrin:

Reply 832

OllyHV

Fairly easy paper, much nicer than January, no horrible show that questions.
Struggled with final part of vectors question, but apart from that was a nice paper.

Reply 833

Cath-ay

Original post by Rotravis

What were the marks for the question 5? I can't see them on your scan.

sorry, ai) 4marks aii) 2marks b) (3marks

Reply 834

Iepnauy

Original post by JulietheCat

It was only up to x^2 so you could safely discard x^3 and x^4 terms. :smile:

I know that now :tongue:

but if I wrote my final answer up to x^4, will I have a mark deducted for not leaving it at x^2 do you reckon? :smile:

Reply 835

ReTurd

Original post by DavidMRoper

i got
dh/ dt = K(2-h)

wheres your extra h come from? :/

That was worth 3 marks for some reason..
All i did was write that as the answer and no working or anything, would i get all 3 marks?

Reply 836

SomeoneIveNeverMet

Original post by LGrosvenor101

Was is |x|<4? Because that's what I put but a few have been saying otherwise haha oh well, it was 1 mark. I never really got them either! That's why if that isn't the answer, I haven't a clue how to get to the answer haha.
Oh I made a silly mistake with the px^2(4-x^2)...on the last line (for some STUPID reason) instead of writing 9/4, I multiplied 9 by 4 and wrote 36 (*facepalm*).
I know that vector question my heart was pounding! I hate vectors, so so much. And then with all the fractions I really thought it was wrong xD

I knew it was Warwick! Woooo! Hahaha my memory isn't so bad after all :tongue:

What grades do you need?
That's okay :tongue:

UCL for Civil Engineering, need A*AA (ouch :frown:

)

Reply 837

Rotravis

Original post by Oromis263

Question 1.
ai)

Unparseable latex formula:

aii)

2lnx + 3ln(x-3) + c

bi)

Unparseable latex formula:

bii)

Unparseable latex formula:

Now\ divide\ the\ function\ previously\ found[br]\[br]\Rightarrow \dfrac{2}{3}x^3 -\dfrac{1}{2}x^2 + 3x -\dfrac{5}{2} ln(2x+1) + c

Where does the 5/2 ln (2x+1) come from? Doesn't the bottom (2x+1) cancel out with the factor on the top, leaving you with 2x^2-x+3?

Reply 838

f1mad

Original post by LGrosvenor101

And oh... I think I remember speaking to you before, again, cannot remember what about! and yes! Warwick for Chemistry xD Sorry, I cannot remember where you said you were going :frown:

I firmed for Warwick; computer-science :tongue:

Reply 839

make it snappy

Original post by mojopin1

I can't really remember now :tongue:

but you first had to differentiate the equation, one part of it needed the product rule. Then you make your dy/dx = 0. Bottom lines cancels and you're left with Y=... Sub that back into the original equation and you get a quadratic which you have to factor, then you get +- 1/3. Then sub these back into your Y=... to get the stationary points.

thatnks for expaining.

that sounds pretty hard, so i don't think i would of managed all that under exam pressure anyway. I differentiated it correctly, i think but thats where i got stuck
:frown: