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OCR C4 (not mei) 18th June 2013 revision

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Reply 580

Namige

Proof there are 3 stationary points for those wondering:

Reply 581

RandomMedic

Original post by a10

but cos x cant be zero the limits of x where greater than zero and less than pi? therefore u can divide by cos?

cosx=0 gives you pi/2 which is within the limits though. The limits are for x, not for cosx

Reply 582

habs10

For the balloon question, for inverse proportion I did 1/k multiplied by Sq. root of R, instead of k/Sq.root R. As a result, I got the answers wrong. But I did the correct integration etc. for the differential equation.

Does anyone know if I lost the whole 9 marks ? :frown:

(( Or will I get error carried forward, and only lose about 2-3 marks? Thanks, I'm really scared, as I need an a*

Reply 583

Jack976

Original post by habs10

(( Or will I get error carried forward, and only lose about 2-3 marks? Thanks, I'm really scared, as I need an a*

I'd guess you should get 4/5 if you subbed in their values to give you a k and c

Reply 584

Namige

Original post by tooambitious

No, because it could be 0, can you divide by 0?

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Trueee,.. owned him

Reply 585

ActaNonVerba

Original post by tooambitious

You haven't disproved what I said. Given that there were three stationary points, you've actually made my point.
One SP was cos(x)=0. Standard C2 level question...

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thought u were saying you couldn't take out cosx.. but yh, I only calculated 2 anyways, we're was the third?

Reply 586

Maid Marian

Original post by Holz888

cosx=0 gives you pi/2 which is within the limits though. The limits are for x, not for cosx

Oh noooo I dropped that value, I completely forgot about it.

Basic error right there :frown:

I let myself down SO much in this exam. So many stupid mistakes caused by me just being stupid and losing my head.

Reply 587

tooambitious

Original post by Namige

Trueee,.. owned him

Don't mean to sound like a prick, just really surprised people are asking this question at C4 level, how did you do C2 :erm:

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Reply 588

Namige

Original post by habs10

(( Or will I get error carried forward, and only lose about 2-3 marks? Thanks, I'm really scared, as I need an a*

It doesn't matter, If you work out 1/k, it will still be the same as k if you did it properly. As it's just a constant.

For example

n = 1/5
1/n = 5

n=5
1/n=5

Reply 589

zmai

Original post by Benjy100

This is effectively a preliminary markscheme until Mr M posts his full definitive solutions. Some of my answers may be wrong. Spoilered incase you don't want to see them :smile:

*A few additions have been made to the markscheme* - namely the cartesian equation (forgot to put it in)

Spoiler

Thankyou!! I forgot to plug x values back in to find y values for question 4.

Would it be okay to write 1/2ln(root3) ? Did they specify the format?

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Reply 590

JakePreedy

Original post by habs10

(( Or will I get error carried forward, and only lose about 2-3 marks? Thanks, I'm really scared, as I need an a*

They never specified that it be C/Sq.root R, so surely 1/(K Sq.root R) is still valid as 1/k is just a constant as is C. All this means is that you're final answer will look different to anyone else who did C/Sq.root R, but may still be a correct answer.

There's still hope!

However, if you did (1/k) * Sq.root R I would imagine you would lose some marks (such as for M1 at the start and the final answer mark), but I think you would get the rest of the marks for such a big question (i.e. error carried forward).

(edited 10 years ago)

Reply 591

ActaNonVerba

Original post by Namige

Trueee,.. owned him

lool calm your tits, I was clearly thinking of something different to you two.. I was just saying you can take it out of the equation to find values for x.. no need for the cheerleading

Reply 592

h2shin

I forgot to sibstitute x back into u, would that cost me 1 or 3 marks?

Reply 593

tooambitious

Original post by ActaNonVerba

thought u were saying you couldn't take out cosx.. but yh, I only calculated 2 anyways, we're was the third?

Cos(x) = 0 where x=PI/2
Sin(x)=1/2 (iirc) where x= 5pi/6 or pi/6

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Reply 594

Jack976

Original post by zmai

Thankyou!! I forgot to plug x values back in to find y values for question 4.

Would it be okay to write 1/2ln(root3) ? Did they specify the format?

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That's fine :smile:

they said a ln b.. No indication that b must be an integer

Reply 595

Namige

Original post by zmai

Thankyou!! I forgot to plug x values back in to find y values for question 4.

Would it be okay to write 1/2ln(root3) ? Did they specify the format?

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Yup, agree with all apart from the volume, which you obviously didn't do lol

Reply 596

Stickyelmo

Original post by h2shin

I forgot to sibstitute x back into u, would that cost me 1 or 3 marks?

Mark scheme isnt that harsh. You'll probably lose 1 since it was the last step.

Reply 597

JakePreedy

Original post by zmai

Thankyou!! I forgot to plug x values back in to find y values for question 4.

Would it be okay to write 1/2ln(root3) ? Did they specify the format?

Posted from TSR Mobile

I think that this would be okay because the question never specified what type of numbers "a" and "b" needed to be (i.e. rational, integer etc.) when in the form a ln(b).