C4 June 2012 - Post Exam Thread - Paper and Solutions in the FIRST POST

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For the Cartesian I left it in the form: (x^2)/3 + ((y-2)^2)/4 =1
As I knew that's the standard equation of an ellipse, is that correct...?
Thanks!

Reply 81

Tomcrease

Original post by MarounD

I have everything right, apart from one concern.

In the cartesian question, I had an answer of 4x² + 3y² -12y = 0

Here's how I got it:

Using the identity Cos(2t) = 2Cos²(t) -1

y would equal 2Cos(2t) + 2

Rearranging gives (y-2)/2 = Cos(2t)

and rearranging the x bit would give Sin(2t) = (x)/sqrt(3)

Then I plugged in those two results into the identity Sin²(2t) + Cos²(2t) = 1

So I got (x²)/3 + (y²-4y+4)/4 = 1

I multiplied the whole equation by 12

Removing 12 from both sides, which eventually gave me 4x² + 3y² -12y = 0

I got this, and it didn't ask for it in a particular form, so I imagine that would still be full marks

Reply 82

JordanS94

I think I got just over 90 UMS :biggrin:

Made a very stupid mistake on 8c :frown:

I did c.p

and taking off about 3 marks from the cartesian equation gives me 66/75 :smile:

Reply 83

ipodcable

hey arsey:

for question 4 if i left it as y^2=6tanx-2 would i lose any marks?
also for 6c) if i multiplied everything out (so i get x^2 and y^2 terms in the equation, do i lose any marks)
for 7c) If for my tables, i did all y values to 2 dp would i lose any marks?

Reply 84

jackegan93

For the Cartesian equation would 4x^2 + 3(y-2)^2 = 12 be acceptable?

I converted the parametric equation for y into terms of cos 2t and then squared it plus the sin2t squared to get a form of cartesian?

Anyone else do this?

Reply 85

sweya

For the last question I did
(10-2lambda)(whatever the rest of the vector was).the co-ordinate of C (amateur error)... Will I lose all 6 marks? I need at least 84!

Reply 86

ayseta

For the very first question I did 'compare x^2' to find the value of B. I think I must have got the same answer as I got the same value for part c. Will that be ok? Thanks for uploading the paper :smile:

Reply 87

mmss

for the cartesian question i think as long as the equation is in terms of x and y only it should be fine. as long as your equation doesnt have any t terms in it

Reply 88

username548498

100%, so happy! Time to focus on fp2! :P Good luck everyone.

Reply 89

Extricated

I thought it was a decent paper but last June was easier IMO and it was 75-100 68-90 61-80 and I know a whole load of people dropped marks on this. I think Arsey is about right with the estimate, probably 73-100 66-90 etc

Reply 90

jackegan93

Original post by mmss

for the cartesian question i think as long as the equation is in terms of x and y only it should be fine. as long as your equation doesnt have any t terms in it

Thanks!

Reply 91

leonb2273

For question 4, I accidentally integrated 1/y rather than y. Other than that, I worked everything else in the question out correctly. How many marks would I get /5 for that question?

Reply 92

melon 314

Arsey how many marks would I lose for working out CP wrong I got a minus mixed up with a plus so I ended up with 4lambda= 24 and therefore worked out P wrong ?

Reply 93

icedragon

Decent paper. Couldn't get the cartesian and that part c) of the binomial expansion I forgot to double one of the terms -.- lol so hopefully 70/75! Cheers Arsey!

Reply 94

ss13

Original post by chaosdestro0

How many marks will I loose if I got A B and C wrong in question one, will I get follow through marks?
It was OK, but that's what worrying me as the grade boundaries might be pretty high. If I dropped 5 marks aside from the question one mistake, do you think that's an A or a B?

i just got B wrong. any ideas on what sort of marks i could get for question one, bearing in mind that part b follows on from part a, and in part a i got A and C but not B right?? HELP ANYONE

Reply 95

Chris P Chicken.

Probably got around a C on this paper. I'm hoping any ways.

Missed out a 7 marker and a 6 marker, didn't even try to answer them. (Part b on implicit differentiation and the last part of the vector question).

Reply 96

Beresford George

Will we get full marks for writing the cartesian equation with arcsin in?

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

Reply 97

Brand New Eyes

Is anyone else disappointed Volume of Revolution and substitution didn't come up? :sadnod:

Also the rate of change question was much easier/simpler than previous ones

Reply 98

chaosdestro0

Original post by ss13

i just got B wrong. any ideas on what sort of marks i could get for question one, bearing in mind that part b follows on from part a, and in part a i got A and C but not B right?? HELP ANYONE

Yeah I just got B wrong actually looking at it.
Wonder this as well.

Reply 99

soempty

I think i screwed up cartesian... maybe i will get marks if my simplification was not required (for y in terms of cos arcsin), so hoping for two in this one.
In question 4 i didn't simplify iirc, but other staff was right.
In implicit differentiation question when i got to the stage xy=3 i written x=1/3y (don't ask me how) and continued working on that, how many marks would i lose?