C1, OCR MEI - 16/05/12 (Answers)

Hey, this is what i got for C1 MEI today.

any discussion/corrections are welcome!

1. y=-2x+7 and (0,7) and (7/2,0)

2. = SQRT(3a/2c)

3. i) 25
    ii) 4/9

4. (x-3)/(x+2)

5. i) 30
   ii) 8/11

6. i) 10
   ii) -720 (x^3)

7. -SQRT(5) < K < SQRT(5)

8. b= -4 c= -8

9. 6n+9 Show that it is always odd and n must be a multiple of 3 for (6n+9)/9

10.i) SQRT(20) = SQRT(20) QED
    ii)1/3 * -3 = -1 QED
    iii) Midpoint AC: (2,2)   Found they intersect at (2,2) and not (5,3) 

11.i) 2x^3 - 5x^2 - 23x - 10
    ii) Cubic graph drawn correct way up passing through -2, -0.5 and 5
    iii) (0,-18)
    iv) (0,-40)

12.i) (4,1) (2.6,-2.6) (0.4,-0.4) give or take 0.1 ish
     ii)Showed
     iii) x= (3+SQRT(5))/2 and (3-SQRT(5))/2

(edited 11 years ago)

Reply 1

Axion

15

Mate your question 8 is wrong. It was b = -4, c = -8.

Reply 2

Jack:)

OP

Original post by Axion

Mate your question 8 is wrong. It was b = -4, c = -8.

Yes, sorry i forgot to make the second equation equal to 85 :smile:

Reply 3

Axion

15

Original post by Jack:)

Yes, sorry i forgot to make the second equation equal to 85 :smile:

lol you remember all of that?

Reply 4

Jack:)

OP

Original post by Axion

lol you remember all of that?

Yep, it’s a shame my pre-exam memory is not that good!
Oh well, it’s only 3 marks tops and hopefully i get a nice examiner and i get a mark for knowing to use simultaneous equations.

Reply 5

Axion

15

Original post by Jack:)

Yep, it’s a shame my pre-exam memory is not that good!
Oh well, it’s only 3 marks tops and hopefully i get a nice examiner and i get a mark for knowing to use simultaneous equations.

Don't worry I know I've lost about 7-8 marks already from stupid mistakes

Reply 6

Jack:)

OP

Original post by Axion

Don't worry I know I've lost about 7-8 marks already from stupid mistakes

Thats the biggest problem with C1, its so easy to make mistakes, i am thinking that the grade boundries will be quite high tho, 60 for an A

Reply 7

dayofs

Original post by Jack:)

Thats the biggest problem with C1, its so easy to make mistakes, i am thinking that the grade boundries will be quite high tho, 60 for an A

For the first one, do we need to write the coordinates of the point where it crosses the axis? I didn't see that -3 from me . :frown:

Reply 8

Georgina :)

HA just got so worried because I didn't recognise ANY answers.. I don't do MEI! :biggrin:

Reply 9

thesaintx

So much love for this. Thank you ever so much

Reply 10

steven hawking

How can you remember all this, geeeeeeeeeeeeeeeeeeeee

Reply 11

tehforum

20

Original post by steven hawking

How can you remember all this, geeeeeeeeeeeeeeeeeeeee

Looks at username...

Lol

Reply 12

steven hawking

Original post by tehforum

Looks at username...

Lol

What about it?

Reply 13

Stephybob

I have an issue with your question 11, if you take the original factorised form of (x+1/2)(x+2)(x-5) then the y intercept would be -5 not -10. I put the equations 2x^3 -5x^2 -23x -10 and the expanded form of the factorised equation into autograph and they aren't the same. So to get from the factorised equation to one with a coefficient of 2, you can't just double everything or I believe you get a false y intercept (but no idea how you actually get there).

So if I'm correct, the answer for the y intercept of f(x) -8 is (0, -13) and the answer to f(x-3) is -20?

Reply 14

Stephybob

Oh and 11ii was to draw the graph of f(x) :smile:

Reply 15

thesaintx

Original post by Stephybob

I have an issue with your question 11, if you take the original factorised form of (x+1/2)(x+2)(x-5) then the y intercept would be -5 not -10. I put the equations 2x^3 -5x^2 -23x -10 and the expanded form of the factorised equation into autograph and they aren't the same. So to get from the factorised equation to one with a coefficient of 2, you can't just double everything or I believe you get a false y intercept (but no idea how you actually get there).

So if I'm correct, the answer for the y intercept of f(x) -8 is (0, -13) and the answer to f(x-3) is -20?

If i'm not mistaken they asked us to put the original factorised form into the form which starts 2x^3 and then to solve from there, so I think the answer's -40 as a result..

Hope it helps

Reply 16

cloudhang

grade boundaries for an A?
how did everyone find it

Reply 17

Jack:)

OP

Original post by Stephybob

Oh and 11ii was to draw the graph of f(x) :smile:

Ty will add that in,

Reply 18

Stephybob

Original post by thesaintx

If i'm not mistaken they asked us to put the original factorised form into the form which starts 2x^3 and then to solve from there, so I think the answer's -40 as a result..

Hope it helps

Hmm you're probably right but seeing as both are f(x) then it shouldn't matter which one you use if they equal the same thing? As both should give the same y intercept? Unless they wanted us to find g(x) or something which has the same roots as f(x) but a different intercept?