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

1. (Original post by Kenna)
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,
arghhhhh im an idiot... thank you -_-
2. (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 can't just divide by cosx and not do cosx = 0

I did:
-4sinxcosx + 2cosx = 0
cosx(2-4sinx)
cosx = 0, sinx = 1/2
3. (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 can't divided by cosx

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4. (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.
when you divide by cos there should only be -4sinx + 2, then rearrange to get sinx=0.5.. then get x=pi/6 and 5pi/6 (only 2 values between 0 and pi)
5. (Original post by Kenna)
The problem I had with the int(tan2x) was that in the formula book it said the int(tanx) is lnIsecxl so, does that mean the int(tan2x) is lnlsec2xl? (it obviously does not now) . But what I'm trying to say is that the "k" coefficient of the tankx is not in the formula book. Unlike the other inegration formulas. So in my opinion it should say int(tankx) is 1/klnlseckxl.

Anyone know what I'm trying to say? lol
Totally agree with this, hence why I just went for ln|sec(2x)|
6. (Original post by tooambitious)
You can't divided by cosx

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You can
7. (Original post by ActaNonVerba)
Did you take -x out as a factor, to prove it was the same as the binomial function?
I'm an idiot, I should have done that! I tried proving the RHS was the LHS by putting -1/x^2 inside of the brackets and seeing if it equaled the LHS. Unfortunately I made a mistake somewhere and couldn't complete the proof and so got this part incorrect. The only part I got correct of 10iii was the expansion part, where I could just use the result they've given and expand it out =/ Hopefully that is 2/4 marks for this part of the question.
8. (Original post by Kenna)
Can't remember exactly, but 30.5 ish?
Damn straight
9. (Original post by ActaNonVerba)
You can
If you divide by cosx you will lose some values of x...
10. (Original post by ActaNonVerba)
You can
No, because it could be 0, can you divide by 0?

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11. (Original post by JakePreedy)
I'm an idiot, I should have done that! I tried proving the RHS was the LHS by putting -1/x^2 inside of the brackets and seeing if it equaled the LHS. Unfortunately I made a mistake somewhere and couldn't complete the proof and so got this part incorrect. The only part I got correct of 10iii was the expansion part, where I could just use the result they've given and expand it out =/ Hopefully that is 2/4 marks for this part of the question.
it would have been easier doing LHS because of all the minus signs :P but I'm sure you'll get a few method marks
12. Can't believe there was no implicit differentiation 8 marker where you find the equation of a tangent, those questions practically give you marks.
13. (Original post by Vip3rgt9)
You're not allowed to divide by cos(x) because it causes you to lose a solution. Cos(x)=0.
but cos x cant be zero the limits of x where greater than zero and less than pi? therefore u can divide by cos?
14. (Original post by tooambitious)
No, because it could be 0, can you divide by 0?

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-4sinxcosx + 2cosx = 0, 4sinxcosx = 2cosx, divide by cosx to get 4sinx = 2, then sinx=0.5..
15. Does anyone have the paper they can upload? Or the marks per question?
16. (Original post by tooambitious)
No, because it could be 0, can you divide by 0?

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Read previous post
17. (Original post by Namige)
If you divide by cosx you will lose some values of x...
Read my last 2 posts
18. i feel unbelievably depressed right now :-(. someone cheer me up!!! i have chem unit 4 tomorrow as well ((
19. (Original post by Dizzy in my Head)
Does anyone have the paper they can upload? Or the marks per question?
HERES THE QUESTION PAPER FOR ANYONE ASKING FOR IT (someone else uploaded these a few posts ago)
http://www.thestudentroom.co.uk/atta...3&d=1371549190
http://www.thestudentroom.co.uk/atta...4&d=1371549203
20. Thank you!

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