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# C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST Tweet

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1. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by masr123)
why are you losers asking eachother questions? there's a markscheme, check the answers and then wait for your results, don't keep asking stupid question, idiot.
such a synaptic(nob). In case you don't understand that's what you're meant to do on post exam discussions
2. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by jmalks)
such a synaptic(nob). In case you don't understand that's what you're meant to do on post exam discussions
not when u have the mark scheme you loser, go to sleep.
3. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST

For Q1,I did everything right except when I opened up the brackets I got 4 instead of 6 at the top.

For Q6e, I drew both graphs properly with the right asymptotes and intersections, but i completely forgot to label which one is which, i also didn't draw y=x.

For 7b, I got up to a point where I had 1/6((x/3)^2+1) but I left it in that form thinking you don't need to simplify it further.

How many marks do you think I will lose altogether?

Thanks a lot.
4. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by joneasy)
ok question 3 where you had to find the x coordinate of the turning point, did you have:

3cos3x + √3sin3x = 0
could be written
cos3x ( 3 + √3 tan3x) = 0
so could you not set the cos3x = 0 then get another answer??
i understand that theres only one x cordinate in the range where the turning point is but if your able to divide by cos 3x then surely you could take it out as a factor??
(Original post by 0range)
If you have then you can divide both sides by . Though normally we avoid dividing by any of sin, cos, tan so that we don't lose solutions but in an equation of this type it can be done.

If we do it in your way, we also get solutions for cos3x=0 which don't satisfy the initial equation. So if you do in this way then at the end check your solutions do they satisfy the initial equation or not.

Sub this in the initial equation,
Hence it doesn't satisfies the equation.
5. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by joneasy)
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(Original post by dsinghdahiya257)
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(Original post by jmalks)
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(Original post by masr123)
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(Original post by sma0414)
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Hey guys, i don't get ums, so if you got 90 ums is that an A, 80 ums a B ect???

thanks
6. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
i found this paper alright actually. The first maths paper that i actually completed and had time to look over.
7. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by fabnt)
two quick questions:

for question 7ai), I wrote my final simplified answer as (2 + ln3x)/(2 rootx)
for question 7b) I wrote my final answer as 1/(2/3x^2 + 6) [although this ends up giving the same numerical value as your answer]
Do you think I will be penalised? And if so how many marks do you reckon I will lose?
Sorry to repost but can anybody answer these questions?
8. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by raheem94)
If you have then you can divide both sides by . Though normally we avoid dividing by any of sin, cos, tan so that we don't lose solutions but in an equation of this type it can be done.

If we do it in your way, we also get solutions for cos3x=0 which don't satisfy the initial equation. So if you do in this way then at the end check your solutions do they satisfy the initial equation or not.

Sub this in the initial equation,
Hence it doesn't satisfies the equation.
Beat me to it haha, you would've explained it better anyway
9. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by raheem94)
If you have then you can divide both sides by . Though normally we avoid dividing by any of sin, cos, tan so that we don't lose solutions but in an equation of this type it can be done.

If we do it in your way, we also get solutions for cos3x=0 which don't satisfy the initial equation. So if you do in this way then at the end check your solutions do they satisfy the initial equation or not.

Sub this in the initial equation,
Hence it doesn't satisfies the equation.
Thank you very much raheem but im still a little confused as to why this doesnt work. I mean if you can set one bracket = to 0 and get a valid answer why would setting the other bracket, i.e. cos3x = to 0 and not get a valid answer??? thank you though i now see that subbing it in doesnt work
10. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by joneasy)
Thank you very much raheem but im still a little confused as to why this doesnt work. I mean if you can set one bracket = to 0 and get a valid answer why would setting the other bracket, i.e. cos3x = to 0 and not get a valid answer??? thank you though i now see that subbing it in doesnt work
Yeah, in an easier way to describe it, its the subtlety when setting cos3x=0, think of it as the way of you cannot be factorising a "zero" out of the initial equation.
11. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by MW94)
Yeah, in an easier way to describe it, its the subtlety when setting cos3x=0, think of it as the way of you cannot be factorising a "zero" out of the initial equation.
Happy days, i realised there could only be one answer so rewrote my solution featuring only the 2n/9 answer. Thank you once again though
12. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
for the one where u get 2pi/9, when writing the value of 3x, do u have to put all of them like arsey did, or can u just put down the one that corresponds to 2pi/3
13. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
Thank you so much (again, as always), Arsey, for the model solutions, has stopped me worrying about it all day!
Almost sure I got 73/75, horrible mistakes:
Q6a, I stupidly wrote Range y is less than OR EQUAL TO 2, damn!! almost definitely lost that one mark, unless they overlook the line accidentally...
And just not entirely sure of the final A1 mark for Q7(b)

Anyways, was a lot better than January, hope everyone else found it ok too

Just now to revise for Grade 8 Theory on saturday (very nervous for it haha!) and C4 next thursday... need to start looking at integration again...
Last edited by fralycis; 15-06-2012 at 01:26.
14. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
Oh crap, I completely missed out a question at the end.
An entire question... I just didn't see it?! Was it on the back page or something? I checked and I couldn't see a question 8 anywhere?
It doesn't actually look that difficult to do. *sigh*

I totalled up my marks and I think I've got 62/75, would that be enough for an A on this paper roughly? I know we don't know precisely yet.
Is there anything I can do about It or am I basically screwed?
This really sucks, no wonder I had so long at the end :////////
15. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by joneasy)
Thank you very much raheem but im still a little confused as to why this doesnt work. I mean if you can set one bracket = to 0 and get a valid answer why would setting the other bracket, i.e. cos3x = to 0 and not get a valid answer??? thank you though i now see that subbing it in doesnt work
Sometimes when you do such things extra solutions are added.

A simple example is,

Multiply both sides by

So extra solutions have been added to the equation which are invalid.

So your one equation is of
So if you think that then will be undefined.

Have i confused you even more?
Last edited by raheem94; 15-06-2012 at 01:41.
16. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by wam-bam)
Hey guys, i don't get ums, so if you got 90 ums is that an A, 80 ums a B ect???

thanks
80UMS: A, 70UMS: B etc. 90UMS is required for an A*
17. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by raheem94)
Sometimes when you do such things extra solutions are added.

A simple example is,

Multiply both sides by

So extra solutions have been added to the equation which are invalid.

So your one equation is of
So if you think that then will become infinite.

Have i confused you even more?
LOL, i love how you're trying confuse him even more than before ^^ + lets keep dividing by 0 as "undefined"
18. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
How many marks would I lose for getting -pi/9 for q3, also would any marks be lost for not drawing the asymptote for q6e after reflection and how many marks lost for getting 18 as the answer to final question
19. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by MW94)
LOL, i love how you're trying confuse him even more than before ^^ + lets keep dividing by 0 as "undefined"
I feel that when you try explaining this to someone he gets even more confused than he was before.

I will edit my 'infinite' to 'undefined'. Thanks for correcting it.
20. Re: C3 June 2012 - Post Exam Thread - Solutions and Paper in the FIRST POST
(Original post by popat06)
How many marks would I lose for getting -pi/9 for q3, also would any marks be lost for not drawing the asymptote for q6e after reflection and how many marks lost for getting 18 as the answer to final question
The asymptote wasn't required, I don't think, as it wasn't specified in the question.
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