Does an Ellipse Intersecting a Circle Result in Imaginary Numbers?

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Discussion Overview

The discussion revolves around the intersection of an ellipse and a circle, specifically examining whether the absence of intersection leads to imaginary numbers for the coordinates involved. The scope includes mathematical reasoning and conceptual exploration of the implications of complex numbers in this context.

Discussion Character

  • Mathematical reasoning
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that if a circle is entirely inside an ellipse, there would be no intersection, leading to the question of whether the coordinates x and y would be imaginary.
  • One participant argues that no intersection implies x must be a complex number, suggesting that substituting x into the equations would yield complex results for both x and y.
  • Another participant suggests that x could be real but greater than the radius R of the circle, which would result in y being purely imaginary.
  • A later reply discusses the possibility of visualizing the situation on an Argand diagram to find geometric reasoning behind the relationships of the coordinates.
  • One participant provides an example with specific equations, showing that in certain cases, y can be purely imaginary while x remains real, indicating that the absence of intersection can lead to complex solutions.

Areas of Agreement / Disagreement

Participants express differing views on the implications of no intersection between the ellipse and the circle, with some asserting that both coordinates must be complex, while others suggest that one can be real and the other imaginary. The discussion remains unresolved regarding the conditions under which x and y take on real or imaginary values.

Contextual Notes

The discussion highlights the dependence on the specific forms of the equations involved and the assumptions about the positions of the ellipse and circle. There are unresolved mathematical steps regarding the conditions that lead to real versus imaginary solutions.

femas
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Hi

Let's say that we have equation of circle as

x2 + y2 = R2

and equation of ellipse in quadratic form as

A x2 + B y2 + Cx + D = 0

if the circle is inside the ellipse, so there is no intersection ...
Are x and y imag in this case? /or/ is one of them imag and the other is real ?... etc.
 
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No intersection would lead to say 'x' being a complex number.

So if you sub x=a+bi into any of the equations you will see that x2 gives a complex number as well, which would lead to 'y' being complex as well.
 
Thank you for the reply.

But 'x' may be real but greater than R which makes 'y' to be pure imaginary.

So I don't know what is the case that makes 'x' real?
 
femas said:
Thank you for the reply.

But 'x' may be real but greater than R which makes 'y' to be pure imaginary.

So I don't know what is the case that makes 'x' real?

Well if you are plotting on the cartesian plane, then I don't think you would see a geometric reason, if you perhaps plot it on an Argand diagram, you might see a geometric reason.
 
rock.freak667 said:
No intersection would lead to say 'x' being a complex number.
Sure it would. Let's look at

[tex]\aligned<br /> \phantom1 x^2+\phantom1 y^2 &= \phantom1 1 \\<br /> 9x^2 + 4y^2 &= 36<br /> \endaligned[/tex]

The solutions (there are four of them) are given by [itex]x^2=32/5[/itex], [itex]y^2=-27/5[/itex]. Note that in this case y is pure imaginary.
 

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