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Mr M's OCR (not OCR MEI) Core 3 answers Jan 2013

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how many out of the 4 would I get for question 8i) I got by differentiation that x=2a, then put this into the equation, I used an equation x^2+4ax+a^2 instead of x^2-4ax+a^2, so I got f(x)>=13a^2 instead of f(x)>=-3a^2 :frown:

At least 2.

Reply 81

KaranbirBandesha

For 7i) if you expanded the bracket 2(y+4) to 2y+8 then cancelled out the 2y's and left it as 8/3 would you get the mark?

Reply 82

Mr M

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Original post by kenann

for 3a i got 5 or -7

A modulus cannot equal a negative number.

Reply 83

Mr M

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Original post by AspiringDoctor

Thank you so much as always!

Just wondering how many marks I've lost if for 3b) I put x > -sqrt2 and 9ii) I forgot to multiply theta by 2 and put my answers as +-35.26?

drop 1 and drop 1

Reply 84

Mr M

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Original post by lonelyknight

My answer for number 8 was squashed into the bottom corner, I hope they'll be able to see it :frown:

We can zoom in!

Reply 85

Mr M

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Original post by Mathmad1

Hi Mr M,

First off i'd like to say thank you for posting all these answers.

I think I may have made a slip on the differentiation for 7)i) and may have ended up with 2(y+3) on the top instead of 2(y+4).

Would I only loose one mark for this? Also I cannot remember if the second part of question 7 is dependent on your answer for 7)i) if so, is Error Carried Forward applied and should I loose marks for my error in the first part?

Finally, for the last question i put 0<= k <= 6. How many marks do you predict I would loose for that?

Thanks again!

7i) drop 1

7ii) drop 0

Last) drop 1

Reply 86

Ecomax

For 3a if i put the two answers as |5| and |-7| is that one mark dropped or? (clearly forgetting to mod each number)

Reply 87

Mr M

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Original post by 1901

Mr M,

For 9)iii. How many marks would k < 3/2 get? I forgot to put anything about the lower bound..

drop 1

Reply 88

Mr M

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Original post by Joe10000

I am probably wrong but for 7i didn't they ask for the differential in Dy/Dx rather than Dx/Dy

Sorry no.

Reply 89

username973061

Is there a copy of the question paper on here anywhere?

Reply 90

Mr M

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Original post by abarlas123

Hi Mr M, first of all thnx loads for putting the answers up, i would really appreciate it if you or someone could tell me what the question was in 3b and 8ii thnx again :biggrin:

Posted from TSR Mobile

3b) Solve

|x-\sqrt 2| => |x + 3\sqrt2|

8ii) Given that fg(3)=69 find a and hence find the x such that g^{-1} (x) = x.

Reply 91

Mr M

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Original post by Theo115

Thank-you very much for copying my answer

Remind me to mark your paper very harshly.

:biggrin:

Reply 92

Mr M

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Original post by gps2601

Would anyone mind running me through 2i)
i've forgotten the question!

If tan A = 2 find cosec A.

Easiest way, draw a right angled triangle. Mark one angle A. Call the opposite 2 and the adjacent 1 so tan A = 2. Find the length of the hypotenuse. Now note that cosec A = hypotenuse / opposite.

Reply 93

Theo115

Original post by Mr M

Remind me to mark your paper very harshly.

:biggrin:

I am sorry, I do not know what came over me...

Reply 94

Mr M

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Original post by JimJam1

Anyone mind explaining how you got the answer to the very last question?

You know

\sin^2 (\frac{\theta}{3})=\frac{k}{6}

\sin (\frac{\theta}{3})=\pm \sqrt{\frac{k}{6}}

You need to make sure you don't take a square root of a negative number and note that

\theta

is less than 90 degrees.

Reply 95

roselle.orleans

Thank you so much for this. I'm quite happy that I got most of the answers except question 7. I know its really unlikely but do you think i atleast get 1 mark for trying to differentiate? I stupidly used the quotient rule instead of product rule cause i started panicking. I was running out of time. :frown:

Reply 96

Snakefingers13

Buggered up the last part. Forgot the angle limits so I had between 0 and 6.

Posted from TSR Mobile

Reply 97

Mr M

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Original post by KaranbirBandesha

For 7i) if you expanded the bracket 2(y+4) to 2y+8 then cancelled out the 2y's and left it as 8/3 would you get the mark?

No that's horrible.

\frac{2(y+4)}{2y+3} \neq \frac{8}{3}

Try letting y = 1.

Reply 98

Mr M

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Original post by Ecomax

For 3a if i put the two answers as |5| and |-7| is that one mark dropped or? (clearly forgetting to mod each number)

Yes drop 1.

Reply 99

Theo115

Original post by Mr M

No that's horrible.

\frac{2(y+4)}{2y+3} \neq \frac{8}{3}

Try letting y = 1.

I do not mean to sound rude, but should you not try to build the self esteem of the students. By saying "No that's horrible" surely will not help the student progress in the world of mathematics. I think perhaps the statement:

"Unfortunatly not, try letting y=1 and you will see that the cancellation does not work. If you would like further questions email me..."

I think this would help the student progress.

Thank-you very much and sorry for sounding rude.

(edited 11 years ago)