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Official Edexcel C3 Discussion Thread watch

1. (Original post by john1234567)
3a) Express 5cosx - 3sinx in the form Rcos(x + a), where R > 1/2 and 0 < a < pi/2.

i worked out R and a correctly but i didn't "express" it in that form - that is, i didn't explicitly say "5cosx - 3sinx = (root34)sin(x + 0.54)", will i lose a mark?
No you won't lose mark, because examiner is looking for the value of R and alpha, but you expressed it inroot34sin(x-alpha)=4 anyways when you tried to find alpha
2. (Original post by dancing.barefoot)
Will I lose marks if I get the right answer but use a different method?

For the x = tan y question:

Then I drew a triangle, put the adjacent side as 1 and the opposite as x, therefore the hypotenuse is . So, since cos y = A/H,

For 9b) I did:

Anybody know if I'll lose marks for that?
I did the same for 9b and don't see why marks would be lost for it In most mark schemes I've seen, there's usually 1 or 2 alternative methods so I don't think you'll lose marks seeing as you got the right answers
3. (Original post by Liverpool F.C.™)
Well looking at previous mark schemes I don't think you'll lose a mark for not writing it in that form.
alright thanks
(Original post by Remarqable M)
No you won't lose mark, because examiner is looking for the value of R and alpha, but you expressed it inroot34sin(x-alpha)=4 anyways when you tried to find alpha
nope i use a different method to find alpha
4. Hi there. Does anyone know where i can find the C3 mark scheme
5. (Original post by Arsey)
Yes, I posted the model solutions on here a few pages back.
how were you able to get the paper and how did you remember all your answers???
6. There's an unofficial one in the C3 discussion thread courtesy of Arsey

The final 'real' one will not be availble for some time
7. (Original post by Arsey)
No one will know the UMS conversions until the results come out. In my opinion this was far harder than any other previous C3 paper; typically C3 isn't that bad and C4 is very hard. I was worried it was going to a tricky paper because of the A* issue and the fact that all of the other papers so far had been pretty straight forward.

Maybe 52/75 is a bit too low but I doubt very much it will be higher than 55/75 for 80UMS.

If it is 55, then you will be looking at 71 - 100UMS; 63 - 90UMS; 47 - 70UMS
yup that seems quite accurate to me!
8. im just hypothesising that more people say its easy on TSR than in general becuase people on this website are more likely to be "nerds" no offence guys (i wish i was a nerd tbh)...on the other hand people who did well on the exam are less likely to post on here, hmm...
9. (Original post by v1oXx-)
Personally, I think it will be about 57ish for an A.
I seriously hope you're right... i did really pants in the exam, and according to the unofficial ms i only got 57 after getting about 97%+ in all the other papers :/ sad times!
10. (Original post by Remarqable M)
ahah i left it like that too my teacher said it is 3 marks.
Lose all 3 marks?

By writing sec x as 1/cos x, show that d(sec x)/dy = secxtanx

How many marks would I lose if I used (cos x)^-1 and differentiated that way.
11. i am such a retard, i didnt even do question 9 cos somehow i just didnt expect there to be anything after question 8. and that is the easiest thing i could've done.
cry
i hope the grade boundaries are loooow
or hello retake of everything.
12. (Original post by Elitist1991)
Appreciate the markscheme, however, for the last question:

so for g(x) = 1 ln(x-1) = 1 therefore, x -1 = e, therefore x = (1 +e)>1

Therefore fg(e+1) = f(1)

therefore fg(x)>=3 . The fact that x>1 for g(x) is irrelevent, as g(x) is the input. to f(x)
Yep ur rite. i got that tooo!
13. (Original post by Milan.)
number 8
you solutions include 45 and 135 i plugged that into the top original equation and you get math error ...
please tell me you dont need those two aswell!!!!!!!
thanks

and number 9
part ii) b) when drawing that graph (x-1)^2 + 3 you can include the value of 3 therefore isn't it fg >= 3

thanks
YES IT SHOULD BEEE =)
14. Comapared to the past papers it was hard. Most of the past papers were easy and I was getting around 90%, on this paper however I am sure I dropped like 15 marks so an A doesn't even seem probable, yet alone an A* which is what I am aiming for. It's gonna have to be a resit I guess..
15. (Original post by sb1234)
Lose all 3 marks?

By writing sec x as 1/cos x, show that d(sec x)/dy = secxtanx

How many marks would I lose if I used (cos x)^-1 and differentiated that way.
You could have done it that way.

16. (Original post by dancing.barefoot)
Will I lose marks if I get the right answer but use a different method?

For the x = tan y question:

Then I drew a triangle, put the adjacent side as 1 and the opposite as x, therefore the hypotenuse is . So, since cos y = A/H,

Anybody know if I'll lose marks for that?
I did that too. Nothing is wrong with what we did. We effectively proved what we had to prove.
17. i expressed

which is neat and correct
18. Silly me!!! I divided by the (x^2 + 1) instead of multiplying the ln part by it. Oh my god ;_; I made a similar mistake in my practice and vowed to never make it repeat... and I did
19. (Original post by john1234567)
i expressed

which is neat and correct
i expressed it that way too!
20. (Original post by john1234567)
i expressed

which is neat and correct
Do you think you would still get the marks if you left it in a correct but messier way?

I didn't simplify it as much as you did

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