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# WJEC C4 17th June 2016

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1. Goodbye, A*.
2. (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

Posted from TSR Mobile
ok so i was really stupid and didn't spot that sin^2x + cos^2x = 1, used the whole rearranged double angle formula to integrate, and then integrated sin2x but i did get 3.73, so i just did it the really long way around, would i still get the 6 marks?
3. Can someone quote me when there is an unofficial mark scheme? Thanks
4. (Original post by nh98)
ok so i was really stupid and didn't spot that sin^2x + cos^2x = 1, used the whole rearranged double angle formula to integrate, and then integrated sin2x but i did get 3.73, so i just did it the really long way around, would i still get the 6 marks?
You probably would. It's still a correct method, and that gets you the marks unless it contradicts explicit instructions in the question.
5. (Original post by Mango88)
I integrated sin2x to get -cos2x/2, is that right?
Yes that's correct. Did you remember to integrate "1" into "x" also? If so, then you must've mistyped the numbers on your calculator - most likely 5/6 marks

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6. (Original post by 98matt)
Yes that's correct. Did you remember to integrate "1" into "x" also? If so, then you must've mistyped the numbers on your calculator - most likely 5/6 marks

Posted from TSR Mobile
Yeah i did!! That's not too bad then, thank you!
7. (Original post by nh98)
ok so i was really stupid and didn't spot that sin^2x + cos^2x = 1, used the whole rearranged double angle formula to integrate, and then integrated sin2x but i did get 3.73, so i just did it the really long way around, would i still get the 6 marks?
Glad I'm not the only one did this. I was happy when others got the same answer 3.73 but when people started mentioning sin^2x + cos^2x = 1, I was thinking I just got really lucky.

Did you get 1/2 + 1/2 somewhere in your integral to get the 1? I think I remember doing that.
8. (Original post by Dominae)
Can someone quote me when there is an unofficial mark scheme? Thanks
Dominae It's up on mathemateg
9. (Original post by EJRicketts)
Dominae It's up on mathemateg
How do you access it?
10. (Original post by EJRicketts)
Dominae It's up on mathemateg
I can't access it aha

Didn't think anybody without an account for the website could either
11. (Original post by Dominae)
Glad I'm not the only one did this. I was happy when others got the same answer 3.73 but when people started mentioning sin^2x + cos^2x = 1, I was thinking I just got really lucky.

Did you get 1/2 + 1/2 somewhere in your integral to get the 1? I think I remember doing that.
It's because you did the Q completely mechanically without thinking lol.
What you did is immediately when you saw cos^2x and sin^2x you converted into
(1±cosx)/2 and then went from there... still right and still all the marks though.
12. (Original post by IrrationalRoot)
It's because you did the Q completely mechanically without thinking lol.
What you did is immediately when you saw cos^2x and sin^2x you converted into
(1±cosx)/2 and then went from there... still right and still all the marks though.
I have the tendency to do that.

But hey, as long as you get the marks right.
13. (Original post by Hopefulmedicesty)
How do you access it?
(Original post by Dominae)
I can't access it aha

Didn't think anybody without an account for the website could either
To access it just make an account and then you have to enrol onto the course, so C4. Use their twitter for the link to the file, make sure you translate as you go along through your browser haha
14. (Original post by EJRicketts)
To access it just make an account and then you have to enrol onto the course, so C4. Use their twitter for the link to the file, make sure you translate as you go along through your browser haha
Somebody just posted a drop box for it on the other thread. I didn't realise anyone could make an account on the site, I thought it was only for students at a specific school Where were you for the C3 exam!?

Also, let's take a moment to appreciate the fact that maths is the same in every language, cause I can't speak/read Welsh for ****.
15. (Original post by EJRicketts)
To access it just make an account and then you have to enrol onto the course, so C4. Use their twitter for the link to the file, make sure you translate as you go along through your browser haha
Thank you !!!!!!!!
16. (Original post by Hydeman)
Goodbye, A*.
17. Mark Scheme: https://www.dropbox.com/s/is5d0l1smt...02016.pdf?dl=0

Question Paper: https://www.dropbox.com/s/h4wwqjjja7...PAPER.pdf?dl=0
18. Buggered up trig somehow cause I'm a simpleton, might have cost me a B grade in this paper but oh well

Reckon I got 47 marks, hopefully which is a C
19. I will wet myself if I found out I have done better in C4 than C3
20. I think this unofficial mark scheme is wrong in one question. They have k/25 being greater than 1. But the maximum value of cosx is 1. So k/25 should be less than or equal to one and greater than or equal to -1. Am I a total idiot or am I right?

EDIT: No I get it now, I misread the question, my bad. It says no solutions, not solutions. That's a mark lost probably.

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Updated: June 19, 2016
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