Finding the Center and Radius of a Circle with Complex Numbers and Loci

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SUMMARY

This discussion focuses on finding the center and radius of a circle defined by the complex equation args((z-3i)/(z+4))=π/6. The correct radius, determined through Pythagorean theorem, is confirmed to be 5 unit². Participants discussed expressing the complex ratio in terms of real and imaginary components, leading to the identification of points on the circle at coordinates (0,3) and (-4,0). The solution emphasizes the importance of transforming complex expressions to derive geometric properties accurately.

PREREQUISITES
  • Understanding of complex numbers and their representation
  • Familiarity with the argument function in complex analysis
  • Knowledge of the inclined angle theorem related to circles
  • Proficiency in using the Pythagorean theorem for geometric calculations
NEXT STEPS
  • Learn how to express complex ratios in terms of real and imaginary parts
  • Study the inclined angle theorem in detail for better geometric insights
  • Explore the properties of loci in complex analysis
  • Investigate the application of complex conjugates in geometric transformations
USEFUL FOR

Students studying complex analysis, mathematicians interested in geometric interpretations of complex functions, and educators teaching advanced mathematics concepts.

Kajan thana
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Homework Statement



Sketch the loci, find centre point and the radius of the circle.
args((z-3i)/((z+4))=π/6[/B]

Homework Equations


args(x/y)=args(x)-args(y)
Circle theorem - inclined angle theorem

The Attempt at a Solution



I sketched the circle with major arc.
Radius= using Pythagorus I got the radius as 5 unit^2 .
H=O/sinθ . H=2.5/sin(π/6)

I am stuck on finding the centre point.

[/B]
 
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Can you find one or two points on the circle?
 
Kajan thana said:

Homework Statement



Sketch the loci, find centre point and the radius of the circle.
args((z-3i)/((z+4))=π/6[/B]

Homework Equations


args(x/y)=args(x)-args(y)
Circle theorem - inclined angle theorem

The Attempt at a Solution



I sketched the circle with major arc.
Radius= using Pythagorus I got the radius as 5 unit^2 .
H=O/sinθ . H=2.5/sin(π/6)

I am stuck on finding the centre point.
[/B]

Your radius is wrong.

Write ##z = x + iy## and express the ratio ##(z-3i)/(z+4)## as ##A(x,y) + i B(x,y)##. How can you get the equation of the curve in terms of the functions ##A(x,y)## and ##B(x,y)##?
 
Ray Vickson said:
Your radius is wrong.

Write ##z = x + iy## and express the ratio ##(z-3i)/(z+4)## as ##A(x,y) + i B(x,y)##. How can you get the equation of the curve in terms of the functions ##A(x,y)## and ##B(x,y)##?
I don't know how to change it into that form.
 
Last edited:
mfb said:
Can you find one or two points on the circle?
The coordinates are (0,3) and (-4,0)
 
Kajan thana said:
I don't know how to change it into that form.
With a complex z and c:$$\frac c z = \frac{cz^*}{zz^*}$$
Here * is the complex conjugation. Now the denominator is real and you can split the fraction into real and imaginary part.
 
mfb said:
With a complex z and c:$$\frac c z = \frac{cz^*}{zz^*}$$
Here * is the complex conjugation. Now the denominator is real and you can split the fraction into real and imaginary part.
I finally got the answer right and the radius is 5 unit^2. Your way gave me the same answer as well.
Thank you so much.
 

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