An ellipse is the image of a circle under a dilation of the plane.
That is, it's a stretching or shrinking of a circle in one direction, relative to the center of the circle.
An ellipse can also be thought of as the image of a particular circle, such as one of radius 1, under a product of two perpendicular dilations of the plane relative to the center of the circle.
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Last updated: 10 June, 2008
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