Sketching Complex Numbers in the Complex Plane

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Discussion Overview

The discussion revolves around sketching complex numbers in the complex plane, particularly focusing on understanding the real and imaginary parts of complex numbers and their representation as conic sections. Participants explore the geometric interpretation of complex numbers and the specific case of the set {z∈C : Rez =|z−2|} being a parabola.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in sketching complex numbers and understanding how subsets translate into conic sections.
  • Another participant questions the process of sketching a specific complex number in the complex plane.
  • There is a discussion about the geometric interpretation of |z - 2| as the distance between a complex number and the real number 2.
  • Participants clarify that the real part of a complex number z can be expressed as x, and the magnitude is calculated using the square root of the sum of the squares of the real and imaginary parts.
  • One participant attempts to simplify the expression involving Re(z) and the distance, leading to a quadratic equation that represents a parabola.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best methods for sketching complex numbers or the interpretation of the specific equation, as the discussion includes various interpretations and approaches.

Contextual Notes

Some participants are still grappling with the definitions and calculations involved in complex numbers, particularly regarding the relationship between the real part and the distance in the complex plane. There are unresolved mathematical steps in the simplification process.

Who May Find This Useful

This discussion may be useful for students new to complex numbers, educators looking for insights into common student difficulties, and anyone interested in the geometric interpretation of complex numbers.

MickeyBlue
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I've just had my first batch of lectures on complex numbers (a very new idea to me). Algebraic operations and the idea behind conjugates are straightforward enough, as these seem to boil down to vectors.

My problem is sketching. I have trouble defining the real and imaginary parts, and I don't understand how some subsets translate into conic sections.

Does anyone have any tips or advice on complex number sketching? (And, specifically, why {z∈C : Rez =|z−2|} is a parabola?)
 
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MickeyBlue said:
I've just had my first batch of lectures on complex numbers (a very new idea to me). Algebraic operations and the idea behind conjugates are straightforward enough, as these seem to boil down to vectors.

My problem is sketching. I have trouble defining the real and imaginary parts, and I don't understand how some subsets translate into conic sections.

Does anyone have any tips or advice on complex number sketching? (And, specifically, why {z∈C : Rez =|z−2|} is a parabola?)

What do you mean? Sketching a number like ##z = 2 + 3i## in the complex plane?
 
MickeyBlue said:
And, specifically, why {z∈C : Rez =|z−2|} is a parabola?
Let z = x + iy
What is Re(z)?

Geometrically |z - 2| represents the distance between an arbitrary complex number and the number 2 (a purely real complex number). How do you calculate the magnitude of a complex number?
 
Mark44 said:
Let z = x + iy
What is Re(z)?

Geometrically |z - 2| represents the distance between an arbitrary complex number and the number 2 (a purely real complex number). How do you calculate the magnitude of a complex number?

x is Re(z). The magnitude is the square root of the sum of the real part squared, and the imaginary part squared. Does this mean that Re(z) = I x + iy - 2I?
 
MickeyBlue said:
x is Re(z). The magnitude is the square root of the sum of the real part squared, and the imaginary part squared. Does this mean that Re(z) = I x + iy - 2I?
Yes. Now can you simplify the right side by finding the magnitude? Note that x + iy - 2 = x - 2 + iy.
 
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Oh, I think I see now. Re(z) = x = I x + iy - 2I. This can be simplified to:

x = √(x-2)2 + y2

x2 = (x-2)2 + y2

0 = y2 - 4x +4

x = ¼y2 + 1

Thank you so much. I must not have taken note of the modulus.
 

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