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WJEC C4 17th June 2016

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1. (Original post by 98matt)
I saw Mathemateg's c3 markscheme. I think I got 68 or 69 /75. I panicked on the circles question and didn't spot it was simple SOHCAHTOA I think c4 went a little better for me today - does anyone know if mathemateg will be doing a markscheme this afternoon or not until Monday?

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I'm hoping I only dropped about 8 overall as well. I hate looking at them though cos you worry loads after seeing full solutions.

The answers themselves are right but method marks are where I might lose them.

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2. (Original post by 98matt)
I first worked out b= 1.5, I don't think that was necessary though. Then I stuck in (A/4)² = A²/1.5t+1

I divided through by A², did a bit of rearranging and got t=10

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ahhhh thats annoying i worked out b and got 1.5 too, then for some stupid reason crossed it out and decided to do it in a weird way..
t=2 when V=A/2 so i put those into the equation
and we needed to find t when V=A/4 which i put as V=1/2(A/2) and then subbed in the expression i had found for A/2

I don't know why I did that haha, oh well!
I'm hoping I only dropped about 8 overall as well. I hate looking at them though cos you worry loads after seeing full solutions.

The answers themselves are right but method marks are where I might lose them.

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Yeah I totally agree! Although I wouldn't worry if you don't have every line of workings exactly like mathemateg's solutions. I think the examiners would award method marks accordingly as you progress through a question, so if you skip a line of workings, they'd more than likely assume your knowledge and award the mark

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4. What did everyone for for the volume of revolution question? And the integration by substitution?
5. (Original post by IrrationalRoot)
Yep 10. You probs just made a mistake in the algebra.
Hey IrrationalRoot, do you think you'll have an unofficial mark scheme up like you did for C3?

Cheers.
6. (Original post by EJRicketts)
Hey IrrationalRoot, do you think you'll have an unofficial mark scheme up like you did for C3?

Cheers.
Well I'll just be here to verify any answers for now, I've got quite a few exams right now so don't really have the time to make an ms.
7. (Original post by Mango88)
What did everyone for for the volume of revolution question? And the integration by substitution?
Volume was 3.73 I believe. Integration by substitution was 38/15.

As I've said before though, there are really no excuses for getting either wrong since your calculator can do the definite integral numerically so you know when you get it right.
8. (Original post by Mango88)
What did everyone for for the volume of revolution question? And the integration by substitution?
The volume of revolution involved two trig equations. You had to spot that:
sin²x+cos²x = 1 (very easy)

sinxcosx + sinxcosx = sin2x (double angle formula thing)

then a simple integration to get 3.73

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9. (Original post by IrrationalRoot)
Well I'll just be here to verify any answers for now, I've got quite a few exams right now so don't really have the time to make an ms.
That's fair, definitely appreciate the help
10. (Original post by its_georgiax)
I got like 5.12 for the volume and 38/15 something like that for the integration
The volume was something like Irrational Roots but I think I got 3.71...
11. (Original post by Maths is Life)
The volume was something like Irrational Roots but I think I got 3.71...
Yeah I wrote out the formula wrong! So I put 2sin X instead of sin 2x, annoying
12. (Original post by 98matt)
The volume of revolution involved two trig equations. You had to spot that:
sin²x+cos²x = 1 (very easy)

sinxcosx + sinxcosx = sin2x (double angle formula thing)

then a simple integration to get 3.73

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I got all the step above right but didn't get that as the final answer, how many marks do you think I lost?
13. (Original post by Mango88)
I got all the step above right but didn't get that as the final answer, how many marks do you think I lost?
If you integrated sin2x incorrectly then you'll probably get 3 or 4/6 marks. If you got the integration completely correct but then typed the numbers on your calculator wrong, probably 5/6

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14. I forgot to multiply my answer by pi so i ended up getting 1.19, do i lose one mark only?
15. Yeah I messed up the volume of rev question.

Had it right up until the end where I didn't simplify 2cosxsinx to sin2x.

So my final answer was 3.12 so annoyingly off
16. (Original post by 98matt)
If you integrated sin2x incorrectly then you'll probably get 3 or 4/6 marks. If you got the integration completely correct but then typed the numbers on your calculator wrong, probably 5/6

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I integrated sin2x to get -cos2x/2, is that right?
17. (Original post by IrrationalRoot)
Volume was 3.73 I believe. Integration by substitution was 38/15.

As I've said before though, there are really no excuses for getting either wrong since your calculator can do the definite integral numerically so you know when you get it right.
was tan(x) = 2 one of the solutions for the trig?
18. (Original post by 98matt)
My guesses for boundaries based on this:
100ums 64-65 / 75
80ums 54/75
70ums 48/75

I think it will be slighly higher than last year's simply because we had more hard past paper qs to prepare. Similar to the difficultly of June 2013 imo

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That's probably pretty accurate just by looking at those grade boundaries i'm like yh definitely considering how hard it was.
19. (Original post by its_georgiax)
Yeah I wrote out the formula wrong! So I put 2sin X instead of sin 2x, annoying
Miss Georgia I made about 10 silly mistakes in C3. Annoying when you could have 100UMS but because you cant do a silly question....
20. (Original post by Firestartc)
was tan(x) = 2 one of the solutions for the trig?
Yes with the other two being (1±sqrt(13))/3.

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