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OCR (not MEI) FP1 10 / 6

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Original post by Kitnimohabbathai

ohh ok so the Imz=-2 is an error? should defo be below? so do you always suppose z= a+bi to solve these? I was using that only to find the centres and stuff....

I don't know. What was the question? Is is from past paper?
Well, you do that when you want to find the point at which the half line starts as well as when you want to find a centre of a circle.

Reply 21

Kitnimohabbathai

Original post by purplemind

For Imz=-2, I don't know why it is above. I think it should be below.
For arg(z-4i) look at this. First you put it in the form arg(z-(a+bi)) then (a,b) is your starting point.
arg(z-4i)=3/4pi
arg(z-(0+4i))=3/4pi
So the starting point is (0,4) which is above the x-axis.

btw when solving equations do you use triangular form? I tend to just cancel out terms and find solutions even with three equations and three unknowns...do you reckon that's ok?

Reply 22

Kitnimohabbathai

it was just an example our teacher used...probably made a mistake....btw how do you draw z + z*=6 on an argand diagram?

Reply 23

purplemind

Original post by Kitnimohabbathai

btw when solving equations do you use triangular form? I tend to just cancel out terms and find solutions even with three equations and three unknowns...do you reckon that's ok?

I'm not really sure what you mean by 'triangular form'.
As long as they don't say they want you to use a particular method and you get all the solutions right, it should be fine.

Reply 24

Kitnimohabbathai

Original post by purplemind

I'm not really sure what you mean by 'triangular form'.
As long as they don't say they want you to use a particular method and you get all the solutions right, it should be fine.

ohhh didn't your teacher teach you triangular form? its the method used in the book too? btw how do you draw z + z*=6 on an argand diagram?

Reply 25

Morgyb96

This may be pretty trivial, but I've got really awful drawing skills; are we allowed to use compasses/protractors to help us to draw the Argand diagrams in the exam?

Reply 26

purplemind

Original post by Kitnimohabbathai

ohhh didn't your teacher teach you triangular form? its the method used in the book too? btw how do you draw z + z*=6 on an argand diagram?

Well maybe I use it but I don't know if it is called a triangular form or not.
To be honest, I don't know what they really want here. From what you give me, I would be able to find Rez=3 or just a point (6,0) which is z+z*.

Reply 27

Kitnimohabbathai

Original post by purplemind

lol that's the answer!! how do you know its Rez=3??

Reply 28

Kitnimohabbathai

Original post by Morgyb96

This may be pretty trivial, but I've got really awful drawing skills; are we allowed to use compasses/protractors to help us to draw the Argand diagrams in the exam?

yeah im sure you are...the drawings don't have to be accurate though right...like the angles and stuff?

Reply 29

purplemind

Original post by Kitnimohabbathai

lol that's the answer!! how do you know its Rez=3??

z+z*=6
Let z=a+bi
Then z*=a-bi
a+bi+a-bi=6
a+a=6
2a=6
a=3
Therefore z=3+bi
(You can't find b from the information you have).
So Re(3+bi)=3 :smile:

Reply 30

Kitnimohabbathai

Original post by purplemind

z+z*=6
Let z=a+bi
Then z*=a-bi
a+bi+a-bi=6
a+a=6
2a=6
a=3
Therefore z=3+bi
(You can't find b from the information you have).
So Re(3+bi)=3 :smile:

thanks so much for all your help!! really appreciate it :smile:

have you done all the past papers? how are you revising for this exam? you seem to know the stuff well...

Reply 31

purplemind

Original post by Kitnimohabbathai

thanks so much for all your help!! really appreciate it :smile:

have you done all the past papers? how are you revising for this exam? you seem to know the stuff well...

You're welcome. :smile:

I have done all the past papers from Jun 05 to Jan 13 (I was doing them from March as we finished the syllabus then). :tongue:

Yes, I'm revising. Right now, I'm doing roots of polynomial equations, then I will do complex number, 3x3 matrices and at the end I will go through the questions on past papers that I did wrong.

Reply 32

Kitnimohabbathai

Original post by purplemind

You're welcome. :smile:

I have done all the past papers from Jun 05 to Jan 13 (I was doing them from March as we finished the syllabus then). :tongue:

Yes, I'm revising. Right now, I'm doing roots of polynomial equations, then I will do complex number, 3x3 matrices and at the end I will go through the questions on past papers that I did wrong.

does anyone know where I can find the grade boundaries for the older papers from jan 2010? is anyone has a list of them or something would really appreciate it...

Reply 33

zcanf

Can anyone help me with June 11 Q10
http://www.ocr.org.uk/Images/60425-question-paper-unit-4725-further-pure-mathematics-1.pdf

I remember when i finally understood this but i can't remember why, can anyone assist me with it?

Reply 34

Music99

Original post by zcanf

Sub the given substitution into the equation and then use exponent rules.

Reply 35

BankOfPigs

Original post by zcanf

What's the problem in particular?

For part 1, just do the substituion of x = u^-1/2
You will get 1/urootu + 3/u +2 = 0
Move the first term to the right and square. Then multiply the whole equation by u^3, and rearrange into the form required

For part 2, it should be quite simple, since after making the substituion, you are just looking for the (-b/a) and then the c/a.