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# Mr M's OCR (not OCR MEI) Core 2 Answers May 2013 watch

1. (Original post by missypink<3)
Shouldn't 9(iii) be 5pie/3 not 4pie/3?
Also how did you get the answer to 7(ii). I got 1.9

7ii) Find the equation of the tangent, then where the tangent meets the x axis. Now calculate the area of the triangle and subtract this from the value of the integral provided previously.
2. (Original post by Mr M)
Of course.
For 7ii) :
I wrote, Area = 37/30 = 1.23 (3sf)
then underlined the decimal, does this lose a mark?
3. (Original post by missypink<3)
I put b as -2 at it was y=4b^x and it crossed the y-axis at (0,4) which is only possible is b is negative.
That's wrong - sorry.

Edit: I should explain why. Try letting for example.
4. (Original post by frankdatank)
For 7ii) :
I wrote, Area = 37/30 = 1.23 (3sf)
then underlined the decimal, does this lose a mark?
That will be ok.
5. (Original post by frankdatank)
For 7ii) :
I wrote, Area = 37/30 = 1.23 (3sf)
then underlined the decimal, does this lose a mark?
Yeah, Mr M said as long as you state 37/30 it's fine.

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6. 67/72 roughly what ums for this paper?

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7. (Original post by Mr M)

7ii) Find the equation of the tangent, then where the tangent meets the x axis. Now calculate the area of the triangle and subtract this from the value of the integral provided previously.
If cosx= -1 then x= 2pie/3
Cosine is negative in the 4th quadrant in the |CAST diagram. Therefore surely you would do pie + 2pie/3 in order to get the value of 5pie/3?

Also for question 7(ii).
I correctly found the equation of the tangent and then integrated the line between 4 and 0. I then subtracted this value from the value found in 7(i).
How many marks would I get?
8. (Original post by germankid101)
For the perimeter question 5(ii) I calculated the length BD using the formula 2rsin(θ/2) which gave me 12.461....
I then added this to 12.8 and 9 to give an answer of 34.3cm (3sf).
How many marks would I lose for this and why isn't this correct?

(Original post by Mr M)
I have no idea where that formula appeared from! Drop 2 marks.
I'm not sure whether you're interested but I suspect the formula works out the length of BC. You know for triangle BAC, and another triangle BDC with D on the circumference of the circle, angle BDC will be half angle BAC, or half theta. From the extended sine rule, the circumcircle of BCD will be the circle with centre A and radius 16 so:

BC/ sin(half theta) = 2R, so BC = 2Rsin(half theta).

However, germankid has made the mistake that D is not on the circumference of the circle.
9. (Original post by missypink<3)
If cosx= -1 then x= 2pie/3
Cosine is negative in the 4th quadrant in the |CAST diagram. Therefore surely you would do pie + 2pie/3 in order to get the value of 5pie/3?

Also for question 7(ii).
I correctly found the equation of the tangent and then integrated the line between 4 and 0. I then subtracted this value from the value found in 7(i).
How many marks would I get?
Don't bother with that CAST rubbish. It is just confusing you.

7ii) drop 3 marks
10. Hi Mr M,

Q1 - I worked out the wrong value value of h (stupid I know) but apart from that my method going forward was fine
Q7ii - I differentiated the equation but made a silly mistake and worked out m as 6 instead of 3. From then on however, my method was fine.
How many marks would I lose?
Akash
11. Mr. M,

Unfortunately on question 3i) I expanded the first binomial incorrectly by using 5C1 and 5C2, as opposed to 6C1 and 6C2. Thus my answer was 64+800x+4000x^2, which I then used in ii) and so got c=-7.25.

How many marks do you think I would lose for this?

Thanks a lot
12. (Original post by metaltron)
I'm not sure whether you're interseted but I suspect the formula works out the length of BC. You know for triangle BAC, and another triangle BDC with D on the circumference of the circle, angle BDC will be half angle BAC, or half theta. From the extended sine rule, the circumcircle of BCD will be the circle with centre A and radius 16 so:

BC/ sin(half theta) = 2R, so BC = 2Rsin(half theta).

However, germankid has made the mistake that D is not on the circumference of the circle.
Yes that'll be it.
13. (Original post by Akash B)
Hi Mr M,

Q1 - I worked out the wrong value value of h (stupid I know) but apart from that my method going forward was fine
Q7ii - I differentiated the equation but made a silly mistake and worked out m as 6 instead of 3. From then on however, my method was fine.
How many marks would I lose?
Akash

drop 1 and drop 2 I expect
14. (Original post by dee1)
Mr. M,

Unfortunately on question 3i) I expanded the first binomial incorrectly by using 5C1 and 5C2, as opposed to 6C1 and 6C2. Thus my answer was 64+800x+4000x^2, which I then used in ii) and so got c=-7.25.

How many marks do you think I would lose for this?

Thanks a lot
drop 2
15. Mr M how many marks would i get for 7ii if i worked out wrong tangent by using wrong x-value, but differentiated correctly, but showed you had to integrate by doing curve- tangent. Therefore, overall wrong area under curve

Also do you get penalised by putting to more decimal places
16. (Original post by Mr M)
Mr M's OCR (not OCR MEI) Core 2 Answers May 2013

1. 6.39 (4 marks)

2. (i) 254 and 106 degrees (3 marks)

(ii) 71.6 and 252 degrees (3 marks)

3. (i) (4 marks)

(ii) c = - 11 (3 marks)

4. (a) (3 marks)

(b) (i) (2 marks)

(ii) a = 2 (3 marks)

5. (i) 62.2 (4 marks)

(ii) 34.0 (4 marks)

6. (i) 963 (3 marks)

(ii) 17 (6 marks)

7. (i) Show ... (4 marks)

(ii) (5 marks)

8. (i) (a) (0, 1) (1 mark)

b) (0, 4) (1 mark)

c) Any value where a > 1 and any value where 0 < b < 1 (2 marks)

(ii) Show ... (5 marks)

9. (i) 15 (2 marks)

(ii) Show f(-0.5)=0 and (6 marks)

(iii) and and (4 marks)

I'll be around a bit this afternoon and then part of this evening to answer questions. Please post in this thread rather than sending me private messages.
RE; 8i), I put y=1 and y=4 as my answers instead of (0,1) and (0,4). Will I still get the marks?
17. (Original post by chuckynoriss)
Mr M how many marks would i get for 7ii if i worked out wrong tangent by using wrong x-value, but differentiated correctly, but showed you had to integrate by doing curve- tangent. Therefore, overall wrong area under curve
curve - tangent will not necessarily produce a sensible answer

You will probably just get 1 mark for differentiating
18. (Original post by martin_brundle)
RE; 8i), I put y=1 and y=4 as my answers instead of (0,1) and (0,4). Will I still get the marks?
No I don't think so. Read the questions more carefully in future.
19. (Original post by Mr M)
drop 2
Hi Mr M,
Do you have a rough idea how many UMS I would get for 68/72?
20. (Original post by missypink<3)
Hi Mr M,
Do you have a rough idea how many UMS I would get for 68/72?
No sorry.

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