Understanding the Ellipse Equation: Cartesian or Polar Coordinates?

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Discussion Overview

The discussion revolves around the classification of the ellipse equation "x=a cos(t); y=b sin(t)" in terms of coordinate systems, specifically whether it is a Cartesian or polar coordinates equation. The scope includes conceptual clarification and mathematical reasoning related to parametric equations of ellipses.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Main Points Raised

  • One participant asks whether the ellipse equation "x=a cos(t); y=b cos(t)" is a Cartesian or polar coordinates equation, noting a suggestion that it may be a transfer from polar to Cartesian.
  • Another participant asserts that it is Cartesian since it provides x and y-axis coordinates.
  • A later reply seeks clarification on the equation, confirming the correct form as "x=a cos(t); y=b sin(t)."
  • One participant explains that if the equations are indeed "x=a cos(t); y=b cos(t)," it would represent a straight line, while the correct form leads to the equation of an ellipse through the relationship of sine and cosine.
  • The distinction between polar and Cartesian coordinates is noted, with a reference to the standard polar equations x=r cos(θ) and y=r sin(θ).

Areas of Agreement / Disagreement

Participants express differing views on the classification of the ellipse equation, with some asserting it is Cartesian and others clarifying the correct parametric form. The discussion remains unresolved regarding the initial confusion over the equation's representation.

Contextual Notes

There is a potential misunderstanding regarding the specific form of the ellipse equation, which could lead to different interpretations. The discussion also highlights the need for precise definitions when transitioning between coordinate systems.

lionelwang
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Hi, guys,

Is the ellipse equation "x=acost; y=bcost" a Cartesian coordinates equation or a polar coordinates equation? Someone said that it's a transfer from a polar one to a Cartesian one.
Need more help on this, thank you very much!
 
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Cartesian I think as you get x and y-axis coordinates.
 
Thanks!
 
lionelwang said:
Is the ellipse equation "x=acost; y=bcost"

You did mean x=a\cos(t),~~y=b\sin(t), right?
 
These are parametric equations giving Cartesian coordinates. If you really mean x= a cos(t), y= b cos(t), you can solve the first equation as cos(t)= x/a so the second equation becomes y= (b/a)x, which graphs as a straight line.

If you meant x= a cos(t), y= b sin(t), as micromass suggests, then x/a= cos(t), y/b= sin(t) so that (x/a)^2+ (y/b)^2= cos^2(t)+ sin^2(t)= 1, an ellipse.

The equations relating polar coordinates and Cartesian coordinates are different but similar: x= r cos(\theta), y= r sin(\theta).
 
Thank you very much, guys.
 

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