How does one get the form of a circle out of this equation?

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Homework Help Overview

The discussion revolves around the problem of sketching the modulus of a complex function, specifically \(|\frac{z+1}{2z+3}|=1\), where \(z=x+iy\). Participants are exploring how to simplify the resulting equation into the standard form of a circle.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the transformation of the modulus equation into a quadratic form and the challenges of completing the square due to the coefficient of \(3\) in \(3x^2\). Some suggest manipulating the equation by dividing to facilitate the completion of the square.

Discussion Status

The conversation is ongoing, with participants providing insights into algebraic manipulation and expressing their struggles with the completion of the square. There is a recognition of the need for further clarification on the specific difficulties encountered.

Contextual Notes

Participants are working under the constraints of homework rules, which may limit the extent of guidance provided. The original poster expresses uncertainty about the simplification process, indicating a need for foundational understanding in manipulating quadratic equations.

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Homework Statement



Sketch modulus((z+1)/(2z+3))=1 on the complex plane where z=x+iy

Homework Equations





The Attempt at a Solution


I know it is a circle but i need help simplifying the equation into the form of a circle.

i'm stuck at
0= 3x^2 + 3y^2 + 10x + 8

I usually complete the square on these type of problems but it has a 3x^2. What can i do to get it to the form of a circle?
 
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If you use Latex, this looks neater:
\left| \frac{z+1}{2z+3} \right| = 1
Play around with the absolute value:
\frac{|z+1|}{|2z+3|} = 1
This means that |z+1|=|2z+3|.
Now substituting a+bi for z, we get |(a+1)+bi|=|(2a+3)+2bi|.
Using the definition of the absolute value of a complex number, we then obtain
a^2+2a+b^2+1=4a^2+12a+9+4b^2
Rearranging yields
3a^2+10a+3b^2+8=0
which you already obtained.
This is a quadratic equation which you can solve to get the imaginary part of z in terms of its real part. Then, plug in values for the real part and get the imaginary part values!
 
Keshroom said:
i'm stuck at
0= 3x^2 + 3y^2 + 10x + 8

I usually complete the square on these type of problems but it has a 3x^2. What can i do to get it to the form of a circle?

If you want to complete the square but can't because of the 3x2 there, what can you do to remove the 3? Divide by it!
 
Keshroom said:

Homework Statement



Sketch modulus((z+1)/(2z+3))=1 on the complex plane where z=x+iy

Homework Equations





The Attempt at a Solution


I know it is a circle but i need help simplifying the equation into the form of a circle.

i'm stuck at
0= 3x^2 + 3y^2 + 10x + 8

I usually complete the square on these type of problems but it has a 3x^2. What can i do to get it to the form of a circle?
That's what you want to do. What specifically is it about completing the square that is a problem for you?
 
DeIdeal said:
If you want to complete the square but can't because of the 3x2 there, what can you do to remove the 3? Divide by it!

ofcause! oh how foolish i am :)

answer:

1/9 = (x+ 5/3)^2 + y^2

thanks guys
 

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