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Homework Help: Describe a circle as an ellipse?

  1. Apr 5, 2005 #1
    Describe a circle as an ellipse??

    An ellipse is a stretched circle. Can you describe a circle as an ellipse? If so, what are the foci of the circle?
    What are the lengths of the minor and major axis?
    Would this circle satisfy the locus definition of an ellipse?

    I really dont know how a circle can be described as an ellipse. If it is possible then how will I find the foci and lengths? There are no numbers? What acutally is the locus definition of an ellipse?

    Please help me get started I dont know what to do. :cry:
  2. jcsd
  3. Apr 5, 2005 #2
    Think of a circle as having 2 axis perpendicular to each other (like an ellipse) that both pass through the center. What can be said about their lengths?

    what is the equation of an ellipse, where does the length of the axis show up in that equation?
  4. Apr 6, 2005 #3
    A circle is a special case of an ellipse where both foci are concentrated at its gravitational center and as a consequence and a characteristic, the length between any point and the foci is always equal.
  5. Apr 6, 2005 #4
    What, pray tell, is a "gravitational center" in terms of euclidean geometry? I wouldn't know quite what to tell a student who wrote about the gravitational center of a circle on a geometry test, without some sort of definition :wink:.

    Anyways, the sentiment is correct: A circle can be described as an ellipse with major and minor axes of equal length, or equivalently as an ellipse with coincident focii.
    Last edited: Apr 6, 2005
  6. Apr 6, 2005 #5
    This is because the only forms that really has a center would be circles an spheres... my definition of a center is a point equally separated from each other points... since we are talking of the circle as an ellipse, I didn’t used the term center. The gravitational center would be the point of "equilibrium” and would be located at a equal distance from each angles…
  7. Apr 6, 2005 #6


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    If you do not know the proper terminology to use in answering such questions, please do not answer them.

    - Warren
  8. Apr 6, 2005 #7
    Sorry folks, if I my terminology really is wrong, I was not aware of it and I appologize...
  9. Apr 6, 2005 #8


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    S'Okay. The "centroid" of a figure ( one, two or three dimensional) is the "center of gravity" treating the figure as if had uniform density. I presumed immediately that that was what you meant by "gravitational center".
  10. Apr 6, 2005 #9
    It is. I didn't meant to give you fallascious terminology. As for Data Euclid does not equal geometry. Mathematicians such as Euler (center of gravity, several theorem on triangles) and Gauss (hyperbolic and parabolic curves) are also pioneers.
  11. Apr 6, 2005 #10
    Certainly true. The geometry of the plane is referred to as Euclidean, though, in reference to his fifth postulate (that noncoincident, parallel lines do not meet).
    Last edited: Apr 6, 2005
  12. Apr 6, 2005 #11
    thanks so much everyone :smile:
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