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# OCR C3 (not MEI) Official Thread - Tuesday 21st June 2016 Watch

1. (Original post by SGHD26716)
Are you sure you are doing OCR. You could be OCR MEI
(Original post by hallo.C)
Are you definitely on the right thread here? I have never seen anything about proof before FP1 in any of my OCR text books.
Yeah I'm definitely not doing MEI and it's at the end of C3 in this textbook (A2 version though I could only find a pic of the AS one)?? I was thinking it was strange there weren't any past paper questions on it so maybe they've just put it in the book even though it's not in the spec idk why they would do that though

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2. Couldn't find an official thread so thought I'd make one

How is everyone finding it? Are you prepared?

Resources:
http://www.ocr.org.uk/qualifications...892-7890-7892/
http://www.physicsandmathstutor.com/...papers/c3-ocr/
3. (Original post by TheTopStudent)
Couldn't find an official thread so thought I'd make one

How is everyone finding it? Are you prepared?

Resources:
http://www.ocr.org.uk/qualifications...892-7890-7892/
http://www.physicsandmathstutor.com/...papers/c3-ocr/
4. Looks like this thread is dying; going to attempt to get it back up...

Here's a lovely question from June '10 that is a good example of OCR putting in traps to test your mathematical awareness (you'll see it when you check the mark scheme for this question...).

5. Hey guys! does anyone know why if an answer to an equation is always positive that means it has two roots? the question i'm talking about that had this situation is https://www.youtube.com/watch?v=S-qI...qtN2_&index=21

all i can think is that if the discriminant is positive then it has two real roots but im not sure how the discriminant is involved in this question?
6. (Original post by buckeybarnes)
Hey guys! does anyone know why if an answer to an equation is always positive that means it has two roots? the question i'm talking about that had this situation is https://www.youtube.com/watch?v=S-qI...qtN2_&index=21all i can think is that if the discriminant is positive then it has two real roots but im not sure how the discriminant is involved in this question?

if tan^2 = a positive number,

tan^2 -[a positive number] = 0

so discriminant (b^2-4ac) would be 0^2-(4)*(1)*(-[a positive number]) which always equals a positive number

so there are 2 roots.
7. (Original post by buckeybarnes)
Hey guys! does anyone know why if an answer to an equation is always positive that means it has two roots? the question i'm talking about that had this situation is https://www.youtube.com/watch?v=S-qI...qtN2_&index=21

all i can think is that if the discriminant is positive then it has two real roots but im not sure how the discriminant is involved in this question?
I am assuming you mean at the end when she rights tan^20=a positive number?

that is because if you then square root that positive number, you get x/- the positive number, thus two roots
8. (Original post by klosovic)
if tan^2 = a positive number,

tan^2 -[a positive number] = 0

so discriminant (b^2-4ac) would be 0^2-(4)*(1)*(-[a positive number]) which always equals a positive number

so there are 2 roots.
Nice method! However, will you need to draw a graph of some description to show that there are two solutions within the given range? (will have a look at m.scheme when I get back home).
9. (Original post by klosovic)
if tan^2 = a positive number,

tan^2 -[a positive number] = 0

so discriminant (b^2-4ac) would be 0^2-(4)*(1)*(-[a positive number]) which always equals a positive number

so there are 2 roots.
that kinda makes sense thank you!
10. (Original post by klosovic)
if tan^2 = a positive number,

tan^2 -[a positive number] = 0

so discriminant (b^2-4ac) would be 0^2-(4)*(1)*(-[a positive number]) which always equals a positive number

so there are 2 roots.
so the tan^2 is the squared term, there is no B term because there isn't a tan and the number without a tan is (a positive number) ? super interesting way to do it!!
11. (Original post by duncant)
I am assuming you mean at the end when she rights tan^20=a positive number?

that is because if you then square root that positive number, you get x/- the positive number, thus two roots
thank you
12. (Original post by rebirth61213)
Looks like this thread is dying; going to attempt to get it back up...

Here's a lovely question from June '10 that is a good example of OCR putting in traps to test your mathematical awareness (you'll see it when you check the mark scheme for this question...).

How is this supposed to trap you, is it part iii ? I thought that was quite a OCR classic by now :P
13. (Original post by danroar)
How is this supposed to trap you, is it part iii ? I thought that was quite a OCR classic by now :P
Do the question, check the mark scheme. You'll see it... (well, it made me go "ohhhhhh" at least)...
14. (Original post by rebirth61213)
Do the question, check the mark scheme. You'll see it... (well, it made me go "ohhhhhh" at least)...
Yeah I got 5/16 pi. Good question. Something you can't just put in the graphics calculator and get an answer
15. (Original post by SGHD26716)
Yeah I got 5/16 pi. Good question. Something you can't just put in the graphics calculator and get an answer
the answer is 1/36 pi.... (for part iii)
16. Anyone have the 2015 paper and MS
17. Ahhh I need to make sure I get 90+ tomorrow, the nerves have kicked in!
18. (Original post by SGHD26716)
Are you sure you are doing OCR. You could be OCR MEI
In theory questions requiring proof by contradiction or disproof by counterexample can be set in any of the A2 units.

In practice, such questions have never been set, except in last Friday's FP3 paper. That was the first time I've ever seen proof by contradiction appear on an OCR maths paper.

(Original post by msulli)
Anyone have the 2015 paper and MS
Paper: http://static1.squarespace.com/stati...+June+2015.pdf
Mark scheme: http://static1.squarespace.com/stati...ark+scheme.pdf
19. (Original post by marioman)
In theory questions requiring proof by contradiction or disproof by counterexample can be set in any of the A2 units.

In practice, such questions have never been set, except in last Friday's FP3 paper. That was the first time I've ever seen proof by contradiction appear on an OCR maths paper.

Paper: http://static1.squarespace.com/stati...+June+2014.pdf
Mark scheme: http://static1.squarespace.com/stati...ark+scheme.pdf
Thanks but thats the 2014 paper
20. (Original post by msulli)
Thanks but thats the 2014 paper
I've just updated my post with the link to the 2015 paper.

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