Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Sometimes you have an ellipse but don't know the center. Finding the center is easy.
The simplest proof is to imagine doing this construction on a circle, the shearing the circle out of shape into an ellipse.
Since you can easily find the center of an ellipse, finding the axes is just as simple.
Given the major and minor axes of an ellipse, you can always find the foci. You need the foci for some construction methods. Just draw radii of length a from the ends of the minor axis.
Given the foci, however, you can't uniquely determine the axes. You need additional information such as the length of one axis. However, the major axis is always along the line through the foci and the minor axis always perpendicularly bisects the line between the foci. |
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Created 28 December 1998, Last Update 12 June 2020