For any non-circular ellipse there is a positive constant *e* < 1 (called the * eccentricity* ), and there are a point (called a

In other words, an ellipse is a set of points the ratio of whose distances from a fixed point and a fixed line is a constant between 0 and 1.

An ellipse has two foci and two corresponding directrices. The constant ratio property applies to either pair.

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Last updated: 10 June, 2008

MATtours project team led by Larry Copes