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

In summary, to sketch the modulus of the complex function ((z+1)/(2z+3))=1 on the complex plane, you can rearrange the equation to obtain 3a^2+10a+3b^2+8=0 and solve for the imaginary part of z in terms of its real part. Then, you can divide by 3 to complete the square and obtain the equation of a circle.
  • #1
Keshroom
25
0

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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  • #2
If you use Latex, this looks neater:
[tex]\left| \frac{z+1}{2z+3} \right| = 1[/tex]
Play around with the absolute value:
[tex]\frac{|z+1|}{|2z+3|} = 1[/tex]
This means that [itex]|z+1|=|2z+3|[/itex].
Now substituting a+bi for z, we get [itex]|(a+1)+bi|=|(2a+3)+2bi|[/itex].
Using the definition of the absolute value of a complex number, we then obtain
[tex]a^2+2a+b^2+1=4a^2+12a+9+4b^2[/tex]
Rearranging yields
[tex]3a^2+10a+3b^2+8=0[/tex]
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!
 
  • #3
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!
 
  • #4
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?
 
  • #5
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
 

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

How do you get the form of a circle from this equation?

The equation for a circle is (x-h)^2 + (y-k)^2 = r^2, where (h,k) represents the center of the circle and r is the radius. To get this form, the equation must be in the form of (x-h)^2 + (y-k)^2 = r^2. If the equation is not already in this form, you may need to complete the square or use other algebraic techniques to get it into this form.

Can any equation be transformed into the form of a circle?

No, not every equation can be transformed into the form of a circle. The equation must contain a variable squared term for both x and y, and cannot contain any cross terms (such as xy). Additionally, the coefficients of the squared terms must be equal.

Why is it important to have an equation in the form of a circle?

The form of a circle is important because it provides information about the center and radius of the circle. This allows us to graph the circle and make predictions about its behavior, such as its size and position on a coordinate plane.

How can I tell if an equation represents a circle or another type of curve?

If the equation is in the form of (x-h)^2 + (y-k)^2 = r^2, then it represents a circle. If not, you can check if the equation contains a variable squared term for both x and y, and if the coefficients of these terms are equal. If both of these conditions are met, then the equation represents a circle.

Can the form of a circle be obtained from a non-linear equation?

Yes, it is possible to transform a non-linear equation into the form of a circle. However, this may require completing the square or using other algebraic techniques to manipulate the equation. It is important to note that not all non-linear equations can be transformed into the form of a circle.

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