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FP1 OCR Post Exam Discussion 11/06/2010

Jeppasloth

What did people get for the summation in terms of n one?

I got 2/3n(2n-1)(n+0.5)

But I think I cocked up somewhere because it looks wrong.

The 'correct' answer... was '1/3n(2n-1)(2n+1)'
... so all you've done is doubled 1/3n (to 2/3n) and halved 2n+1 (to n+0.5).
You'll lose max 1 for that.. maybe even none xD

Reply 141

for no reason

Revolution is my Name

I got n/3(2n-1)(2n+1) I think. And I think that's right because I fiddled around with the sum of the first few terms and it came to the same as that suggested by the formula.

Wooo!! I got the same as you :biggrin:

Reply 142

I0144

Jeppasloth

Did you get 2/3n(n^2-0.5)?

Because thats what I got, I realised how to factorise when the guy said put your pens down. Managed to write that **** down though.

I got 1/3n(4n^2-1)

4n^2-1 is a difference of two squares so it would be: (2n+1)(2n-1)

so final answer is 1/3n(2n+1)(2n-1)

shame i put 1/3n(4n^2-1) in the exam lol

Reply 143

someone4325823

1

nikita_atikin

I put anticlockwise rotation of -60 round centre (0,0) and clockwise rotation of 60 round centre (0,0). I put both of them. Will I be penalised or not? It is technically the same thing written in two different ways... :s-smilie:

"Clockwise rotation of 60 degrees, centre (0,0)" is correct.
"Anticlockwise rotation of -60 degrees" is also correct, if a little random.
You'll get the marks. xD

Reply 144

Jeppasloth

2

Anticlockwise of 300 degrees right too?

Reply 145

for no reason

Jeppasloth

Anticlockwise of 300 degrees right too?

Yep.. you people are innovative :biggrin:

Reply 146

someone4325823

1

Jeppasloth

Anticlockwise of 300 degrees right too?

Yes. ... Just hope that the examiner realises it's right too. xD

Reply 147

Jing_jing

14

I0144

I got 1/3n(4n^2-1)

4n^2-1 is a difference of two squares so it would be: (2n+1)(2n-1)

so final answer is 1/3n(2n+1)(2n-1)

shame i put 1/3n(4n^2-1) in the exam lol

Ah drat, I didn't factorise this fully either D8
The longer I stay on this thread, the more marks I realise I've lost! :p:

Reply 148

729

Pretty Easy on the whole i thought :smile:

Reply 149

R0BMAN

I found it fine personally, I lost a few silly marks where I didnt add a minus and stuff like that but on the whole I answered every question because I knew how to do it, I didnt guess any of them. My friends found it hard so Im quite happy about my answers. The only one I can think I might have screwed up was the summing one - which I would have considered to be the easiest one before the exam, but I ended up with like 1/3(4n^3 + 4n + 1) or something like that. Not quite sure where I went wrong there but I couldnt see how to factorize it further so it must have been wrong.

What did people get for the polynomial roots question? I got x^2 + 4kx + 4k ... my mate reminded me after that it should have been -4kx, because of -b/a or something, which makes sense, should only lose one mark on that one though.

Reply 150

purplestarfish

I0144

I got 1/3n(4n^2-1)

4n^2-1 is a difference of two squares so it would be: (2n+1)(2n-1)

so final answer is 1/3n(2n+1)(2n-1)

shame i put 1/3n(4n^2-1) in the exam lol

reckon 1/3n(n+1/2)(n-1/2) is okay?

(n + 1/2 ) = (2n + 1)

Reply 151

purplestarfish

R0BMAN

I found it fine personally, I lost a few silly marks where I didnt add a minus and stuff like that but on the whole I answered every question because I knew how to do it, I didnt guess any of them. My friends found it hard so Im quite happy about my answers. The only one I can think I might have screwed up was the summing one - which I would have considered to be the easiest one before the exam, but I ended up with like 1/3(4n^3 + 4n + 1) or something like that. Not quite sure where I went wrong there but I couldnt see how to factorize it further so it must have been wrong.

What did people get for the polynomial roots question? I got x^2 + 4kx + 4k ... my mate reminded me after that it should have been -4kx, because of -b/a or something, which makes sense, should only lose one mark on that one though.

i got the same as u, x^2 + 4kx + 4k.. heard one of them was meant to be a minus too, shouldnt be penalised too heavily for that though.

Reply 152

nosignature

for no reason

Why are you stalking the FP1 thread?

He's doing it 'for no reason'

Anyone still need answers? I have them now?

Reply 154

StephS1

urghh i screwed up on this summations question too but i was just lookin at the mark scheme to a question like this and i reckon we'd still get 4/6 as long as the examiner doesnt just see our wrong answer and write us off completely. in the mark scheme one of the points actually says 'attempt' to factorise, so hopefully we'll still get the majority of the marks :s-smilie:

Reply 155

snowman18992

Mr M

Anyone still need answers? I have them now?

Yes Please :biggrin:

Reply 156

StephS1

mr m if we got the wrong final answer due to a silly expansion error how many marks outta 6 do u think we would get?

OCR (not OCR MEI) FP1 Answers June 2010

1. Prove by induction (5 marks)

2. (i) (-7) (2 marks)

(ii)

\begin{pmatrix} -7 & -20 \\ 11 & -20 \end{pmatrix}

(4 marks)

3.

\frac{n(2n-1)(2n+1)}{3}

(6 marks)

4. (i) modulus = 13 argument = 1.18 (4 marks)

(ii)

\frac{-11}{85} - \frac{27i}{85}

(3 marks)

5. (a)

\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}

(2 marks)

(b) (i) Stretch in x direction scale factor 5

(ii) Rotation clockwise about the origin by pi/3 (2 marks)

6 (i) (a) Circle centre 3 - 4i radius 5 (2 marks)

(b) Vertical line with Re(z)=3 (2 marks)

(ii) Shade region inside circle and to the right of the line (2 marks)

7

x^2 -4kx + 4k = 0

(7 marks)

8 (i) Show (2 marks)

(ii)

\frac{\sqrt{n+1} + \sqrt {n+2} - 1 - \sqrt{2}}{2}

(6 marks)

(iii) Does not converge as sqrt of infinity = infinity (1 mark)

9 (i)

a(a-1)

(3 marks)

(ii) (a) Inconsistent

(b) Consistent but no unique solution

(c) Consistent with unique solution

10 (i)

z = 2 + i

(5 marks)

(ii) Show (1 mark)

(iii)

w = 2 -i

(5 marks)

Edit: tidied up a bit

Reply 158

729

Mr M

OCR (not OCR MEI) FP1 Answers June 2010

1. Prove by induction (5 marks)

2. I will edit this later to make it look nice (can't remember how to do matrices in LaTeX and my school network is blocking the TSR wiki!):

(i) (-7) (2 marks)

(ii) 2 x 2 matrix top row -7 - 20 bottom row 11 -20 (4 marks)

3.

\frac{n(2n-1)(2n+1)}{3}

(6 marks)

4. (i) modulus = 13 argument = 1.18 (4 marks)

(ii)

\frac{-11}{85} - \frac{27i}{85}

(3 marks)

5. (a) 2 x 2 matrix top row 0 1 bottom row 1 0 (2 marks)

(b) (i) Stretch in x direction scale factor 5

(ii) Rotation clockwise about the origin by pi/3 (2 marks)

6 (i) (a) Circle centre 3 - 4i radius 5 (2 marks)

(b) Vertical line with Re(z)=3 (2 marks)

(ii) Shade region (2 marks)

7

x^2 -4kx + 4k = 0

(7 marks)

8 (i) Show (2 marks)

(ii)

\frac{\sqrt{n+1} + \sqrt {n+2} - 1 - \sqrt{2}}{2}

(6 marks)

(iii) Does not converge as sqrt of infinity = infinity (1 mark)

9 (i)

a(a-1)

(3 marks)

(ii) (a) Inconsistent

(b) Consistent but no unique solution

(c) Consistent with unique solution

10 (i)

z = 2 + i

(5 marks)

(ii) Show (1 mark)

(iii)

w = 2 -i

(5 marks)

Shout if you disagree with something as I haven't checked my work yet.

For number 7 i think i got x^2 - 4k^2x - 4k^2

Reply 159

purplestarfish

Mr M

OCR (not OCR MEI) FP1 Answers June 2010

1. Prove by induction (5 marks)

2. I will edit this later to make it look nice (can't remember how to do matrices in LaTeX and my school network is blocking the TSR wiki!):

(i) (-7) (2 marks)

(ii) 2 x 2 matrix top row -7 - 20 bottom row 11 -20 (4 marks)

3.

\frac{n(2n-1)(2n+1)}{3}

(6 marks)

4. (i) modulus = 13 argument = 1.18 (4 marks)

(ii)

\frac{-11}{85} - \frac{27i}{85}

(3 marks)

5. (a) 2 x 2 matrix top row 0 1 bottom row 1 0 (2 marks)

(b) (i) Stretch in x direction scale factor 5

(ii) Rotation clockwise about the origin by pi/3 (2 marks)

6 (i) (a) Circle centre 3 - 4i radius 5 (2 marks)

(b) Vertical line with Re(z)=3 (2 marks)

(ii) Shade region (2 marks)

7