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Complex number lock FP2 help!

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Could someone possibly help with 12ii?
I have no idea where to start


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Reply 1
Original post by Mutleybm1996
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Could someone possibly help with 12ii?
I have no idea where to start


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I need the Cartesian equation found earlier first
Original post by Mutleybm1996

Could someone possibly help with 12ii?
I have no idea where to start


1. By the way arg works we have: arg(zazb)=θarg(za)arg(zb)=θ\arg (\frac{z-a}{z-b}) = \theta \Rightarrow \arg(z-a) - \arg(z-b) = \theta

2. zaz-a is the complex number that takes us from fixed point a to arbitrary point z. Here z is restricted to the circumference of a circle.

3. arg(za)\arg(z-a) measures the angle that this complex number makes with the +ve x-axis.

4. By circle geometry, you should know that the angle subtended by any point on the circumference of a circle between two fixed points (i.e. in an arc) is constant.

Does that give you a clue?
Original post by TeeEm
I need the Cartesian equation found earlier first


ImageUploadedByStudent Room1421941519.251929.jpg
here, thank you

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(edited 9 years ago)
Reply 4
Original post by Mutleybm1996
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here, thank you

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arg[(z-a)/(z-b)]

arg(z-a)- arg(z-b)=θ

arg(z-6-√3) -arg(z-6+√3) = θ


sub the point they give you in the above equation to get θ
(edited 9 years ago)
Original post by TeeEm
arg[(z-a)/(z-b)]

arg(z-a)- arg(z-b)=θ

arg(z-6-3i) -arg(z-6+3i) = θ


sub the point they give you in the above equation to get θ

Thanks :smile:
Could i also ask you about q9?
I tried some bits and bobs but got stuck

ImageUploadedByStudent Room1421942431.942244.jpg
ImageUploadedByStudent Room1421942448.982117.jpg


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Reply 6
Original post by Mutleybm1996
Thanks :smile:
Could i also ask you about q9?
I tried some bits and bobs but got stuck

ImageUploadedByStudent Room1421942431.942244.jpg
ImageUploadedByStudent Room1421942448.982117.jpg


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my reply is incorrect as I am skipping between pages look at the correction below


arg[(z-a)/(z-b)]

arg(z-a)- arg(z-b)=θ

arg(z-6-3√3) -arg(z-6+3√3) = θ


sub the point they give you in the above equation to get θ


you should get theta = pi/2
(edited 9 years ago)
Original post by TeeEm
my reply is incorrect as I am skipping between pages look at the correction below


Changed it, thank you.
Could you possibly look at Q9? (In a post earlier)
Reply 8
Original post by Mutleybm1996
Changed it, thank you.
Could you possibly look at Q9? (In a post earlier)


substitute z = x + iy and carry out the algebra

this is straight forward


look at some questions in the link


http://www.madasmaths.com/archive/maths_booklets/further_topics/various/complex_numbers_part_2_exam_questions.pdf


there many questions with solutions oncomplex but they are mixed in topics.
At least 40 questions on complex loci all mixed up/the booklet gets progressively harder.
Original post by TeeEm
substitute z = x + iy and carry out the algebra

this is straight forward


look at some questions in the link


http://www.madasmaths.com/archive/maths_booklets/further_topics/various/complex_numbers_part_2_exam_questions.pdf


there many questions with solutions oncomplex but they are mixed in topics.
At least 40 questions on complex loci all mixed up/the booklet gets progressively harder.


The algebra still isn't working out :/


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Reply 11
Original post by Mutleybm1996
The algebra still isn't working out :/


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here are the first three lines

then you should be able to complete it

|x+iy-k2c|=k|x+iy-c|

|(x-k2c)+iy|=k|(x-c)+iy|

(x-k2c)2+y2=k2[(x-c)2+y2]
Original post by TeeEm
here are the first three lines

then you should be able to complete it

|x+iy-k2c|=k|x+iy-c|

|(x-k2c)+iy|=k|(x-c)+iy|

(x-k2c)2+y2=k2[(x-c)2+y2]


If c=a+bi why have you factored(maybe not the right term) it into the real part of the equation?


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Reply 13
Original post by Mutleybm1996
If c=a+bi why have you factored(maybe not the right term) it into the real part of the equation?


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does it say c is complex?
Original post by TeeEm
does it say c is complex?


"Where C=a+bi For any fixed complex number"


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Reply 15
Original post by Mutleybm1996
"Where C=a+bi For any fixed complex number"


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sorry I did not see it
the method is still the same

put z=x+iy
c = a +bi

group real and imaginary inside the mods
"apply" the mods
square both sides (careful you do not forget to square the k on the right and then multiply the whole RHS by k2)
then a big mess to simplify.

this is nothing but an exercise in concentration.

good luck
Original post by TeeEm
arg[(z-a)/(z-b)]

arg(z-a)- arg(z-b)=θ

arg(z-6-√3) -arg(z-6+√3) = θ


sub the point they give you in the above equation to get θ


Quick question, why did you substitute those specific values into a and b? Why didn't you switch it round?
EDIT: sorted that part

Okay, so I've split it into the two arg sections, what do I do now?

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(edited 9 years ago)
Reply 17
Original post by Mutleybm1996
Quick question, why did you substitute those specific values into a and b? Why didn't you switch it round?


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answer to (a) this is where the arc meets the x axis

answer to (b) if I put it these values the other way round theta will be -pi/2 which gives exactly the same equation, if you multiply it by -1 (I am not sure if this is what you are asking)
Original post by TeeEm
answer to (a) this is where the arc meets the x axis

answer to (b) if I put it these values the other way round theta will be -pi/2 which gives exactly the same equation, if you multiply it by -1 (I am not sure if this is what you are asking)


Could you run through what to do after the arg's have been separated? I can't seem to get pi/2


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Reply 19
Original post by Mutleybm1996
Could you run through what to do after the arg's have been separated? I can't seem to get pi/2


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wait 2 minutes please

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