Mr M's OCR (not OCR MEI) Core 3 Answers June 2012

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Reply 80

jamieward

70/72 if M.M is right god damn 9 last part, really wanted 98 UMS

Reply 81

Mr M

Study Forum Helper

Original post by Antonton

Mr M how much will you lose for omitting the PI from volumes of revolution?

drop 1

Reply 82

c_subs

Original post by Mr M

Why can't you integrate logarithms?

You know how to do it by parts (I hope) and you certainly know how to do from part (i) of the question!

well my teacher said a while back - when learning C3 that you can't ln ln when i asked.

I know you can ln ln by parts, but that C4, hence why put a C4 way of working if it's supposed to be C3, otherwise the exam should be called C4 not C3.
And yes, someone already said the same thing that you last said, but if you see my new reply, i can get the answer except +3 instead of +1

Reply 83

MP1805

Original post by c_subs

'i've just tried to work it out now, and Instead of +1 i got +3,
here i'll show you partly what i've done to get +3, idk where's gone wrong:
-->plug limits into 'yln(2y) - y'
the yln(2y) gives [when plug in limits]: 1/2 x {(e⁴ln[2e⁴]) - e⁴}

it is ln(2y) therefore, ln(2 * 0.5e^4) which would give you ln(e^4) = 4

so 0.5e^4 * 4 = 2e^4 - 0.5e^4 = 1.5e^4 then with the limit 0.5 I get:

0.5 * 0 - 0.5 = -0.5 so overall answer is 0.5(3e^4 + 1)

(edited 11 years ago)

Reply 84

c_subs

if someone can be bothered, can you right down the steps for me on Q9, or mainly Q9ii, thanks

Reply 85

Mr M

Study Forum Helper

Original post by Next Level

Hey Mr.M cheers for the answers! How many marks would I drop for integrating (e^x + 2)^2 (with limits 1 and 0) as (e^x + 2)^3/3e^x, with the limits subbed in and simplified to an expression in terms of e?

Probably nothing - sorry!

Reply 86

Mr M

Study Forum Helper

Original post by Matt osbourne

How many marks would i lose for only putting the solution x<4/3 for Q1?
I couldn't expand out brackets properly :tongue:

drop 2 marks probably

Reply 87

19hannah94

Hi Mr M,
Thanks for the answers!

Was wondering, for 4b, why is the denominator 2 as i thought integrating the function (e^x+2)^2 wopuld give you a denominator of 3 after you +1 and recipricol the new power?

Also, do you remember the equation of the lines in question 1 as I'm normally fine with this method but seem to have the answers wrong.

Thanks

Reply 88

Mousebudden

Original post by Mr M

Yes 2 or 3 marks for knowing that.

Please answer I asked you on the first page lol

On question 9iii) if I used my answer from question 9ii) to calculate the volume (but followed the correct method) would I get any of the 2 marks?

Also, on question 9ii) I got an incorrect answer as when I substituted in the limits I rewrote ln(e^4) as e^4 instead of 4. However, I applied the limits correctly to the other variables. (And applied the correct method throughout) How many marks out of the 6 is this likely to have costed me?

Thanks a lot

(edited 11 years ago)

Reply 89

kubs

Mr M for 4b, I realised that (e^x + 2)^2 should be written as two brackets and expanded, and then I integrated but got the wrong answer.. 10. Something I think.. How many marks would I get?
Also, for the last question, 9iii, I didnt square the radius but did Pi x radius x height, and then took away the volume of the shaded. Would I get any marks?
Thanks a bunch :-)

Reply 90

c_subs

Original post by MP1805

it is ln(2y) therefore, ln(2 * 0.5e^4) which would give you ln(e^4) = 4

yh so you get ln2+4, but all of that needs to multiply by e⁴
because you plug in all limits into 'yln(2y) -y'

Reply 91

Next Level

Original post by Mr M

Probably nothing - sorry!

So I'd drop all the marks? :frown:

How is it meant to be integrated? :confused:

Reply 92

tallguitarist

ok, i think that i got 61-63, would this be enough for 90 UMS?

Reply 93

MP1805

Original post by Mr M

Probably nothing - sorry!

Mr M why doesnt chain rule work for this type of question? :confused:

Reply 94

Morkike

what will be full UMS at a geuss anyone?

Reply 95

Super Mario 64

Original post by Mr M

I'm off home now but will answer some more questions later (in about one hour).

Thanks so much for the answers.

Few questions..

For 4b) I used the chain rule to integrate instead of expanding the brackets. Would I get any method marks for this?
For 6ii) I got 0.183 and then put 'therefore 0.18' - would I lose marks for rounding down?
For 9iii) I tried to use volume of revolution to work it out (Didn't see the cylinder trick) But ended up with the wrong answer. Would I gain a method mark for this?

Sorry for so many questions. Post exam nerves you see...

Thanks in advance. Much appreciated :smile:

Reply 96

MP1805

Original post by c_subs

yh so you get ln2+4, but all of that needs to multiply by e⁴
because you plug in all limits into 'yln(2y) -y'

The y limit is 0.5e^4 and 0.5

Reply 97

Mr M

Study Forum Helper

Original post by Next Level

So I'd drop all the marks? :frown:

How is it meant to be integrated? :confused:

Simplest way is to expand the brackets and integrate term by term.

Reply 98

adamjay

Does anyone know the full question for Q5 b) ?

Thanks :smile:

Reply 99

Mousebudden

Original post by Mr M

Simplest way is to expand the brackets and integrate term by term.

PLEASE reply haha

On question 9iii) if I used my answer from question 9ii) to calculate the volume (but followed the correct method) would I get any of the 2 marks?

Also, on question 9ii) I got an incorrect answer as when I substituted in the limits I rewrote ln(e^4) as e^4 instead of 4. However, I applied the limits correctly to the other variables. (And applied the correct method throughout) How many marks out of the 6 is this likely to have costed me?

Thanks a lot