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# OCR C4 (not mei) 18th June 2013 revision watch

1. (Original post by Vip3rgt9)
I put 8.something as well but they were actually vectors, they have length, they weren't lines that continued forever.

EDIT: By the way I don't know what the correct answer is.
Yeah I understand that, but what I said still stands. If you draw any two lines that meet, whether they carry on or don't there will always be two angles to measure
2. (Original post by Benjy100)
It's odd because although I don't know whether AB dot AC (what I did) or BA dot AC was required I got 171.3 degrees but then went on to say - thus acute angle is 8.68 degrees - does it even matter which one you do? I'm not too sure about this one really - I mean it makes sense to think that AB dot AC leads you to the angle BAC just by drawing the diagram - so now I thinking I am thinking that I should have just stayed with 171.3 degrees. Then again I may have even taken the wrong dot product so who knows. I guess we'll have to wait for Mr M
The answer you got will not affect the answer to the second part of the question, but it surely the diagram that you drew would explain how the angle had to be 8.68 degrees. The only reason is because I draw the points on the Cartesian graph and it was very small indeed, so I went for 8.68 degrees. Who knows :P
3. That paper was horrible! I really need an a to meet my offer, but after that there's no way!

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4. Such a tricky paper for me, but then again a lot of the very intelligent people in my class said it was tricky as well, so hopefully low grade boundaries! Had a go at everything question anyway so might get a few method marks here and there
5. (Original post by a10)
is that even possible?
Why not? Angles in a trainagle always add up to 180, therefore it can be split up into literally any combination of 3, as long as it all added up to 180. One angle could be 179.9999999996, it's just the sides will therefore be very large... but will still be a triangle.
6. (Original post by Holz888)
Yeah I understand that, but what I said still stands. If you draw any two lines that meet, whether they carry on or don't there will always be two angles to measure
So did you do 360-ans?
7. (Original post by Benjy100)
Yes but there is only one angle between a pair of sides of a pyramid. We were not dealing with mere lines in this case we were dealing with an angle with a fixed value which you could highlight by moving a pen along the sides BA and then AC of the pyramid. and measuring the angle. I'm not too sure what went on with this question now haha but anyway I gave both 171.3 and the acute angle which they may allow.
Yup but at this point, they weren't asking for the angle within the pyramid, or they would have asked for the angle within the pyramid it was just a basic 'work out the angle' question, for which there is always two answers on the mark scheme (unless they ask for acute)
8. (Original post by Theo115)
The answer you got will not affect the answer to the second part of the question, but it surely the diagram that you drew would explain how the angle had to be 8.68 degrees. The only reason is because I draw the points on the Cartesian graph and it was very small indeed, so I went for 8.68 degrees. Who knows :P
Haha yes in that case 8.68 may be correct then (in fact both answers may well be correct). Anyway I messed up the volume because I kept thinking there had to be a right angled triangle for the base when really it was just a matter of 0.5absinC
9. Predictions for a* raw mark???
10. what people put for initial volume of balloon?
11. (Original post by ActaNonVerba)
what people put for initial volume of balloon?
30.5
12. (Original post by ActaNonVerba)
what people put for initial volume of balloon?
Can't remember exactly, but 30.5 ish?
13. For the stationary points:

Everyone saying they get 3 answers, i have no idea how you guys are working it out.

the way i did it, which is wrong but i cant see where i went wrong is:

-2sin2x +2cosx = 0

sin2x=2sinxcos

-4sinxcosx + 2cosx = 0

(divide by cosx)

-4tanx + 2 = 0

tanx = 0.5

which is more than wrong but where did i go wrong?

and i do believe in the question it did say, Find the stationary point.

Not Find the stationary points.
14. (Original post by Vip3rgt9)
So did you do 360-ans?
I got 8 out as my first answer
15. (Original post by tooambitious)
I'm sorry, but I completely disagree. What you've said actually makes no sense. When there is an easier paper, it's difficult to differentiate between the top and bottom students becaus even th bottom students can do all the questions, consequently, the results are dependent on who makes the fewest silly mistakes.
Certainly your claim that there will be no difference between top and bottom is rubbish, considering many people at my centre thought the paper was fine and some thought it was awful.
The paper was hard but the questions really weren't as 'left field' as you're making out

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I totally agree with you. These non-conventional questions will truly separate the wheat from the chaff, only the best will get them, and the rest will not get their heads around it and therefore fail. Grade boundaries will surely be around mid to low 50s for this paper.
16. (Original post by Maid Marian)
I just can't believe I forgot what inversely proportional meant

That's going to haunt me forever. 9 marks down the drain.

Did the same thing :|
17. (Original post by Kirity)
For the stationary points:

Everyone saying they get 3 answers, i have no idea how you guys are working it out.

the way i did it, which is wrong but i cant see where i went wrong is:

-2sin2x +2cosx = 0

sin2x=2sinxcos

-4sinxcosx + 2cosx = 0

(divide by cosx)

-4tanx + 2 = 0

tanx = 0.5

which is more than wrong but where did i go wrong?

and i do believe in the question it did say, Find the stationary point.

Not Find the stationary points.
You're not allowed to divide by cos(x) because it causes you to lose a solution. Cos(x)=0.
18. (Original post by Kirity)
For the stationary points:

Everyone saying they get 3 answers, i have no idea how you guys are working it out.

the way i did it, which is wrong but i cant see where i went wrong is:

-2sin2x +2cosx = 0

sin2x=2sinxcos

-4sinxcosx + 2cosx = 0

(divide by cosx)

-4tanx + 2 = 0

tanx = 0.5

which is more than wrong but where did i go wrong?

and i do believe in the question it did say, Find the stationary point.

Not Find the stationary points.
If you divide -4sinxcoxs by cosx you get -4sinx not -4tanx. What you do is factorise out a -2cosx. So -2cosx(2sinx-1) Then solve each one from there,
19. Do you get error carried forward marks? I don't remember.
20. (Original post by max25)
Predictions for a* raw mark???
Hoping something low

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